DeviceIOControl returns false with error 87, or error1...WHY??

Hi,
I am developing a virtual device driver (VxD), in Windows 98.
I need to know how we use DeviceIOControl to call a function , that is lying in the VxD.

It gives me (win32 Error codes)
error no. 1: Invalid Function. (when I place the function name as the second parameter, and the function code in a header file).

and when I make the second parameter null, it gives me
error no. 87: Parameter Incorrect.

What is the problem here?
Any suggestions??
I'll mail my code, if anyone so requires.
Thanks.