Access Violation by calling function in dll

Hello,
who can help me ???
I develop an application for PocketPC 2003 with eMbedded Visual C++
4.0 and  use a dll, which e.c. has an function to open maps (*.shp)
and Orthophotos (georeferenced JPGs).
While testing the application, I saw, that there is a problem by
opening JPGs. The debugger shows the following message:

First-change exception in <meineAnwendung>.exe: 0xC0000005: Acess
Violation

The exception comes, when the function in the dll is called:

bool CGeoPADCtrl::GeoPAD1(BSTR filePath) 
{
	bool (PASCAL *fun1)(BSTR FilePath);
	//GetProgAddress gets Adress of the function in the dll
	(FARPROC&)fun1 = GetProcAddress(hInstasnce,_T("GeoPAD1"));
	
	if(fun1)
		//calles the function
		return fun1(filePath);	 <-- here occurs the exception 
	
	return false;
}

Can anybody say me, what's the reason for such an exception ???
Is the error in the dll, and if yes, how could I repair it ???

Please give me your soon answer, I'm happy about every answer !!!!

Sandra