IIS: Calling GetProcAddress on ISAPI filter failed

I am attempting to write a very simple ISAPI filter for debugging another issue. IIS is returning error code 0x8007007f with Calling GetProcAddress on ISAPI filter "the dll here" failed

I'm using C++ without MFC in Visual Studio 2012 on Windows 7 with IIS 7.5.

Below is a snippet of the code. While debugging, it doesn't appear to call the HttpFilterProc. I manually added a def file to the project, but I don't know if it's actually getting used.

Any ideas on the cause?

DWORD WINAPI __stdcall HttpFilterProc(HTTP_FILTER_CONTEXT *pfc, DWORD NotificationType, VOID *pvData)
{
   switch (NotificationType)
   {
   case SF_NOTIFY_SEND_RESPONSE :
         return DoSendResponse(pfc, (HTTP_FILTER_SEND_RESPONSE *) pvData);
   default :
         break;
   }
   return SF_STATUS_REQ_NEXT_NOTIFICATION;
}


DWORD DoSendResponse(HTTP_FILTER_CONTEXT * pfc,HTTP_FILTER_SEND_RESPONSE * pResponse)
{
   BOOL fServer = TRUE;
   DWORD dwServerError;
   fServer = pResponse->SetHeader(pfc, "UMFilter:", "Enabled");
   if ( !fServer )
   {
         dwServerError = GetLastError();
         pfc->pFilterContext = (LPVOID)(DWORD64)pResponse->HttpStatus;
   }
   return SF_STATUS_REQ_NEXT_NOTIFICATION;
}

The solution was to explicitly add the Module Definition file into the project properties -> Linker -> Input Property page in VS2012.

The Linker wasn't picking up the file I added.