how to catch the error of InvokeHelper

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C++

Hello:
In some computer,i call the function of InvokeHelper failed,but i don't get any error message,While in others it succeed.

 static BYTE parms[] = VTS_BSTR VTS_PVARIANT VTS_PVARIANT VTS_PVARIANT VTS_PVARIANT ;  
try
{
  InvokeHelper(0x68, DISPATCH_METHOD, VT_EMPTY, NULL, parms, URL, Flags, TargetFrameName, PostData, Headers);
}
catch (COleDispatchException* pException)
{
   CString strErrorMsg;
   pException->GetErrorMessage(strErrorMsg.GetBuffer(256), 256);
   strErrorMsg.ReleaseBuffer();
   AfxMessageBox(strErrorMsg);
}
catch(...)
{
  CString strErrorMsg = "some error has happened";
  AfxMessageBox(strErrorMsg);
}