>I'm trying to call a function that returns a structure. If I just execute the function without assigning the return value to a variable there's no problem. But if I try assigning to a variable I get the message "Function argument value, type, or count is invalid."

I'd try setting the variable to a string equal to the length of the returned structure first. For some other info and maybe a helpful tip, try http://support.microsoft.com/default.aspx?scid=kb;en-us;181289