Unlock Account on Active Directory

Question

I'm experiencing some problems when unlocking a locked account on AD.

I'll keep it very simple. I'm assuming that the account is currently locked.

 

 UserPrincipal oUserPrincipal = ADMethods.GetUser("test.user");  
 
oUserPrincipal.UnlockAccount();  
 oUserPrincipal.Save();  

oUserPrincipal is returned using an Admin account on the AD though a PrincipalContext using

Now ..

oUserPrincipal.UnlockAccount(); is generating an exception System.UnauthorizedAccessException

When checking the logs on the "Test AD server", it's returning a failed negotiation stating that "test.user" is locked out. Since I'm returning a user principal using an admin account, why is unlockAccount method generating an error?

Would appreciate your help. attached please find the entire class

 

here's the exception:

 
 System.UnauthorizedAccessException: Access is denied.
   at System.DirectoryServices.Interop.UnsafeNativeMethods.IAds.SetInfo()
   at System.DirectoryServices.DirectoryEntry.CommitChanges()
   at System.DirectoryServices.AccountManagement.SDSUtils.WriteAttribute(String dePath, String attribute, Int32 value, NetCred credentials, AuthenticationTypes authTypes)
   at System.DirectoryServices.AccountManagement.ADStoreCtx.WriteAttribute(Principal p, String attribute, Int32 value)
   at System.DirectoryServices.AccountManagement.ADStoreCtx.UnlockAccount(AuthenticablePrincipal p)
   at System.DirectoryServices.AccountManagement.AccountInfo.UnlockAccount()
   at UnlockApp.Form1.UnlockUserAccount(String sUserName) in C:\Users\christian.debono\Documents\Visual Studio 2010\Projects\UnlockApp\UnlockApp\Form1.cs:line 78
   at UnlockApp.Form1.UnlockButton_Click(Object sender, EventArgs e) in C:\Users\christian.debono\Documents\Visual Studio 2010\Projects\UnlockApp\UnlockApp\Form1.cs:line 45
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Button.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)