1813
The specified resource type cannot be found in the image file.

What could cause this error?

dllhinst is a validated instance handle of the dll
IDD_DIALOG is in both the DLL as in the program 1 and the dialog has resource identifier
IDD_DIALOG
htab is the window handle of which the dialog will be the child of (validated)
tmail is a DLGPROC function

hdlg = CreateDialog(dllhinst,MAKEINTRESOURCE(IDD_DIALOG), htab,(DLGPROC)tmain);

hdlg returns NULL, raises error 1813 and no dialog box is created.

I really don't know what is wrong, any help is greatly appreciated...