Marshal.FreeHGlobal Failure

Question

Hello,
I am fairly new to all this and I am hoping somone can help.  I am writing a C# application that requires use of the Clipborad for inter-process communication.  C# has methods I can leverage in order to accomplish this:

 

 Clipboard.SetText(string);

Unfortunately, there is an unacceptable delay when using this call.  The receiving process does not recognize its presence for over 5 seconds.  As such, moved onto native Win32 SDK calls.  Namely:  SetClipboardData() and its required support functions.  This call gives me the speed I require as the contents are transferred near immediately to the clipboard when I use the native methods.  Unfortunately, the call to free allocalted heap memory failes like clockwork on the fourth iteration.
When I comment out the FreeHGlobal function (bad juju...), everything operates as expected.  Here is the class I use to use native methods:

 
class ClipboardHelper
{
[DllImport("user32.dll")]
static extern bool OpenClipboard(IntPtr hWndNewOwner);
[DllImport("user32.dll")]
static extern bool EmptyClipboard();
[DllImport("user32.dll")]
static extern IntPtr SetClipboardData(uint uFormat, IntPtr hMem);
[DllImport("user32.dll")]
static extern bool CloseClipboard();
[DllImport("kernel32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
public static extern IntPtr GlobalFree(IntPtr handle);

// Metafile mf is set to a state that is not valid inside this function.
static public bool PutTextOnClipboard(IntPtr hWnd, StringBuilder s)
{
   bool bResult = false;
   if (OpenClipboard(hWnd))
   {
      IntPtr ptr = Marshal.StringToHGlobalAnsi(s.ToString());

      if (EmptyClipboard())
      {
         IntPtr hRes = SetClipboardData(1, ptr);
         CloseClipboard();
      }
      Marshal.FreeHGlobal(ptr);
      //GlobalFree(ptr);
   }
   return true;

}

The top level exception is:

 
An unhandled exception of type 'System.StackOverflowException' occurred in mscorlib.dll

Does anyone have any idea what I am doing wrong here?
Partial stack trace:

 

 mscorlib.dll!System.AccessViolationException.AccessViolationException() + 0x14 bytes 
  [Native to Managed Transition] 
  [Managed to Native Transition] 
  mscorlib.dll!System.Reflection.CustomAttributeEncodedArgument.ParseAttributeArguments(System.Reflection.ConstArray attributeBlob, ref System.Reflection.CustomAttributeCtorParameter[] customAttributeCtorParameters, ref System.Reflection.CustomAttributeNamedParameter[] customAttributeNamedParameters, System.Reflection.RuntimeModule customAttributeModule) + 0x5b bytes 
  mscorlib.dll!System.Reflection.CustomAttributeData.CustomAttributeData(System.Reflection.RuntimeModule scope, System.Reflection.CustomAttributeRecord caRecord) + 0x4c4 bytes 
  mscorlib.dll!System.Reflection.CustomAttributeData.GetCustomAttributes(System.Reflection.RuntimeModule module = {System.Reflection.RuntimeModule}, int tkTarget) + 0x53 bytes 
  mscorlib.dll!System.Reflection.CustomAttributeData.GetCustomAttributesInternal(System.Reflection.RuntimeAssembly target = {System.Reflection.RuntimeAssembly}) + 0x47 bytes 
  mscorlib.dll!System.Reflection.RuntimeAssembly.GetCustomAttributesData() + 0x5 bytes 
  mscorlib.dll!System.Reflection.CustomAttributeData.GetCustomAttributes(System.Reflection.Assembly target) + 0x21 bytes 
  mscorlib.dll!System.Resources.ManifestBasedResourceGroveler.GetNeutralResourcesLanguage(System.Reflection.Assembly a = {System.Reflection.RuntimeAssembly}, ref System.Resources.UltimateResourceFallbackLocation fallbackLocation = MainAssembly) + 0x31 bytes 
  mscorlib.dll!System.Resources.ResourceManager.CommonSatelliteAssemblyInit() + 0x6d bytes 
  mscorlib.dll!System.Resources.ResourceManager.ResourceManager(string baseName, System.Reflection.Assembly assembly = {System.Reflection.RuntimeAssembly}) + 0x51 bytes 
  mscorlib.dll!System.Environment.ResourceHelper.GetResourceStringCode(object userDataIn) + 0x111 bytes 
  [Native to Managed Transition] 
  [Managed to Native Transition] 
  mscorlib.dll!System.Environment.ResourceHelper.GetResourceString(string key, System.Globalization.CultureInfo culture) + 0xd1 bytes 
  mscorlib.dll!System.Environment.GetResourceStringLocal(string key) + 0x48 bytes 
  [Native to Managed Transition] 
  [Managed to Native Transition] 
  mscorlib.dll!System.Runtime.InteropServices.COMException.COMException() + 0x14 bytes 
  [Native to Managed Transition] 
  [Managed to Native Transition] 
  mscorlib.dll!System.Runtime.InteropServices.Marshal.FreeHGlobal(System.IntPtr hglobal) + 0x74 bytes