Error message regarding exception unhandled Help

Question

Hi

I have developed a application which is in its testing phase the application runs well in most time but in one or two computer specifically i am getting this every time i run the application on them .............Please help me to fix the bug...
i am posting the error message below...........

************** Exception Text **************
System.NullReferenceException: Object reference not set to an instance of an object.
   at ComputerLabMangementProject.FormLogOut.FormLogOut_Load(Object sender, EventArgs e)
   at System.Windows.Forms.Form.OnLoad(EventArgs e)
   at System.Windows.Forms.Form.OnCreateControl()
   at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
   at System.Windows.Forms.Control.CreateControl()
   at System.Windows.Forms.Control.WmShowWindow(Message& m)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
   at System.Windows.Forms.ContainerControl.WndProc(Message& m)
   at System.Windows.Forms.Form.WmShowWindow(Message& m)
   at System.Windows.Forms.Form.WndProc(Message& m)
   at ComputerLabMangementProject.FormBaseLabMangement.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

************** Loaded Assemblies **************
mscorlib
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4200 (NetFxQFE.050727-4200)
    CodeBase: file:///C:/Windows/Microsoft.NET/Framework/v2.0.50727/mscorlib.dll
----------------------------------------
ComputerLabMangementProject
    Assembly Version: 1.0.0.0
    Win32 Version: 1.0.0.0
    CodeBase: file:///C:/Program%20Files/Default%20Company%20Name/LAbManagementClient/ComputerLabMangementProject.exe
----------------------------------------
System.Windows.Forms
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4016 (NetFxQFE.050727-4000)
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Windows.Forms/2.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4205 (VistaSP2GDR.050727-4200)
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System/2.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System.Drawing
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4016 (NetFxQFE.050727-4000)
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Drawing/2.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------
System.Configuration
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4016 (NetFxQFE.050727-4000)
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Configuration/2.0.0.0__b03f5f7f11d50a3a/System.Configuration.dll
----------------------------------------
System.Xml
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4016 (NetFxQFE.050727-4000)
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Xml/2.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
System.Data
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4016 (NetFxQFE.050727-4000)
    CodeBase: file:///C:/Windows/assembly/GAC_32/System.Data/2.0.0.0__b77a5c561934e089/System.Data.dll
----------------------------------------
System.Data.DataSetExtensions
    Assembly Version: 3.5.0.0
    Win32 Version: 3.5.30729.1 built by: SP
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Data.DataSetExtensions/3.5.0.0__b77a5c561934e089/System.Data.DataSetExtensions.dll
----------------------------------------
System.Core
    Assembly Version: 3.5.0.0
    Win32 Version: 3.5.30729.1 built by: SP
    CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Core/3.5.0.0__b77a5c561934e089/System.Core.dll
----------------------------------------
System.Transactions
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4016 (NetFxQFE.050727-4000)
    CodeBase: file:///C:/Windows/assembly/GAC_32/System.Transactions/2.0.0.0__b77a5c561934e089/System.Transactions.dll
----------------------------------------
System.EnterpriseServices
    Assembly Version: 2.0.0.0
    Win32 Version: 2.0.50727.4016 (NetFxQFE.050727-4000)
    CodeBase: file:///C:/Windows/assembly/GAC_32/System.EnterpriseServices/2.0.0.0__b03f5f7f11d50a3a/System.EnterpriseServices.dll
----------------------------------------

Please help me to fix the bug......any advice will be highly honoured

Sam Hobbs · Answer

Is that subkey documented? Does it say it needs to be created? My guess is that it is not documented. Probably there is a documented API that you could use and should use instead.

raj · Answer

Hi all i have fixed the bug the issues was with registry sub key actually any computer which is new and have never used the usb mass device the subkey usbstor is not created and hence i was getting error for only some specific computer ...... now i have fixed the bug i now check wether the subkey exits or not if not exist i create the subkey and hence no null refferrence..........

raj · Answer

Hi Marimuthu i have caught where the exception occurs it is in the registry read or write operation the lines given below Registry.LocalMachine.OpenSubKey(@SYSTEM\CurrentControlSet\Services\USBSTOR true).SetValue(Start 4) ; Registry.CurrentUser.OpenSubKey(@Software\Microsoft\Windows\CurrentVersion\Policies\Explorer true).SetValue(StartMenuLogoff 1); Registry.CurrentUser.OpenSubKey(@Software\Microsoft\Windows\CurrentVersion\Policies\Explorer true).SetValue(NoClose 1); if ((int)Registry.LocalMachine.OpenSubKey(@SYSTEM\CurrentControlSet\Services\USBSTOR true).GetValue(Start) == 3); all other subsequent registry read wwrite operation line...... if i comment all such registry read write code than the error goes away......therefore it is sure that the proplem is in the code for registry read write but i find no clue as how to fix it as i have written such registry read write code but never faced such exception a quick help will be highly apreaciated

raj · Answer

Hi i can upload the project but i dont think u can run it since it needs a data base ......... cant u help me by going through the code i can suggest you to remove all refference to othr form and try loading this form

Marimuthu Arigovindasamy · Answer

Can u upload ur full project. I can't compile this code and find where is the pbm. As per the error message pbm is in the FormLogOut_Load event only.

raj · Answer

here is the code for FormLogout please go through it using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using Microsoft.Win32; using System.Threading; using System.Diagnostics; namespace ComputerLabMangementProject { public partial class FormLogOut : FormBaseLabMangement { public FormLogOut() { InitializeComponent(); } private void FormLogOut_Load(object sender EventArgs e) { string userType; // TODO: This line of code loads data into the 'databaseDataSetGetUserType.Users' table. You can move or remove it as needed. this.usersTableAdapter.Fill(this.databaseDataSetGetUserType.Users); userType = this.usersTableAdapter.GetUserTypeQuery(Program.frmLogin.UserName).ToString(); //disposes keyboard hook Program.kh.Dispose(); //shows Task bar Taskbar.Show(); if (userType != Administrator && userType != Faculty) { //this will disable pen drive Registry.LocalMachine.OpenSubKey(@SYSTEM\CurrentControlSet\Services\USBSTOR true).SetValue(Start 4); //MessageBox.Show(Pen); //this refresh registry //System.Diagnostics.Process.Start(@c:\windows\System32\RUNDLL32.EXE user32.dll UpdatePerUserSystemParameters); } if(userType!=Administrator) { //this line will edit registry for removing log off and turn off from xp start menu i have disabled for testing in vista Registry.CurrentUser.OpenSubKey(@Software\Microsoft\Windows\CurrentVersion\Policies\Explorer true).SetValue(StartMenuLogoff 1); Registry.CurrentUser.OpenSubKey(@Software\Microsoft\Windows\CurrentVersion\Policies\Explorer true).SetValue(NoClose 1); //Put code to disable task manager Process[] myProcesses; // Returns array containing all instances of Explorer. myProcesses = Process.GetProcessesByName(explorer); foreach (Process myProcess in myProcesses) { //myProcess.CloseMainWindow(); myProcess.Kill(); } System.Diagnostics.Process.Start(@Explorer.EXE); } if ((int)Registry.LocalMachine.OpenSubKey(@SYSTEM\CurrentControlSet\Services\USBSTOR true).GetValue(Start) == 3) this.ButtonRequestUsb.Enabled = false; } private void ButtonChangePassword_Click(object sender EventArgs e) { FormChangePassword frmChangepassword = new FormChangePassword(); DialogResult resultChangePassword = frmChangepassword.ShowDialog(); /*if (frmChangepassword.Sucess == 1) { this.Activate(); frmChangepassword.Dispose(); } else*/ if (resultChangePassword == DialogResult.Cancel) { this.Activate(); frmChangepassword.Dispose(); } } private void ButtonLogOff_Click(object sender EventArgs e) { DialogResult Sure = MessageBox.Show(Are You Sure You Want to Log off Machine Alert MessageBoxButtons.YesNo); if (Sure == DialogResult.Yes) { FormFeedback frmFeedBack = new FormFeedback(); frmFeedBack.ShowDialog(); if (frmFeedBack.LogOutStatus) { //MessageBox.Show(LOgoff); Registry.LocalMachine.OpenSubKey(@SYSTEM\CurrentControlSet\Services\USBSTOR true).SetValue(Start 3); Registry.CurrentUser.OpenSubKey(@Software\Microsoft\Windows\CurrentVersion\Policies\Explorer true).SetValue(StartMenuLogoff 0); Registry.CurrentUser.OpenSubKey(@Software\Microsoft\Windows\CurrentVersion\Policies\Explorer true).SetValue(NoClose 0); ShutDown.Exit(0 4); } else { if (frmFeedBack.FeedBack) { frmFeedBack.Dispose(); this.Activate(); this.Show(); } else { frmFeedBack.Activate(); frmFeedBack.Show(); } } } else this.Activate(); } private void ButtonTurnOff_Click(object sender EventArgs e) { DialogResult Sure = MessageBox.Show(Are You Sure You Want to Turn off Machine Alert MessageBoxButtons.YesNo); if (Sure == DialogResult.Yes) { FormFeedback frmFeedBack = new FormFeedback(); frmFeedBack.ShowDialog(); if (frmFeedBack.LogOutStatus) { //MessageBox.Show(Turn Off); Registry.LocalMachine.OpenSubKey(@SYSTEM\CurrentControlSet\Services\USBSTOR true).SetValue(Start 3); Registry.CurrentUser.OpenSubKey(@Software\Microsoft\Windows\CurrentVersion\Policies\Explorer true).SetValue(StartMenuLogoff 0); Registry.CurrentUser.OpenSubKey(@Software\Microsoft\Windows\CurrentVersion\Policies\Explorer true).SetValue(NoClose 0); ShutDown.Exit(1 0); } else { if (frmFeedBack.FeedBack) { frmFeedBack.Dispose(); this.Activate(); this.Show(); } else { frmFeedBack.Activate(); frmFeedBack.Show(); } } } else this.Activate(); } private void ButtonSignOut_Click(object sender EventArgs e) { DialogResult Sure = MessageBox.Show(Are You Sure You Want to Sign Out off Machine Alert MessageBoxButtons.YesNo); if (Sure == DialogResult.Yes) { FormFeedback frmFeedBack = new FormFeedback(); frmFeedBack.ShowDialog(); if (frmFeedBack.LogOutStatus) { Registry.LocalMachine.OpenSubKey(@SYSTEM\CurrentControlSet\Services\USBSTOR true).SetValue(Start 3); Registry.CurrentUser.OpenSubKey(@Software\Microsoft\Windows\CurrentVersion\Policies\Explorer true).SetValue(StartMenuLogoff 0); Registry.CurrentUser.OpenSubKey(@Software\Microsoft\Windows\CurrentVersion\Policies\Explorer true).SetValue(NoClose 0); Application.Restart(); } else { if (frmFeedBack.FeedBack) { frmFeedBack.Dispose(); this.Activate(); this.Show(); } else { frmFeedBack.Activate(); frmFeedBack.Show(); } } } else this.Activate(); } private void ButtonRequestUsb_Click(object sender EventArgs e) { this.ButtonRequestUsb.Enabled = false; Thread usbThread = new Thread(new ThreadStart(ClassUsbRequest.Request)); usbThread.Start(); } public delegate void EnableButtonUsbRequest(bool b); public void changeEnable(bool a) { if (this.ButtonRequestUsb.InvokeRequired) { this.ButtonRequestUsb.Invoke(new EnableButtonUsbRequest(this.changeEnable) true); } else this.ButtonRequestUsb.Enabled = a; } } } I am also giving the code for BaseForm which the logOutform inherits using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; namespace ComputerLabMangementProject { public partial class FormBaseLabMangement :Form { protected override void WndProc(ref System.Windows.Forms.Message m) { try { if (m.Msg != 0x0010) { base.WndProc(ref m); } else { //Windows has send the WM_CLOSE message to your form. //Ignore this message will make the window stay open. } } catch (Exception ex) { MessageBox.Show(error no 0001); LogAppend.Append(ex.ToString()); } } public FormBaseLabMangement() { InitializeComponent(); } } } Please try to help me now............ I am unable to catch in which line the error is.........But i can undertand that this error is with regard to windows messaging to my application

Marimuthu Arigovindasamy · Answer

Can u post the code and mention in which line u r getting this error message. Reason for the pbm: when Object value is null when u r accessing the object's function it will throw this error. For an example DateTime dateT = null; when I access dateT.ToString() it throws error.