Vanilla Doom "cannot open" wad

[DuckReconMajor]

For some reason, whenever I make a single level wad and try to open it in vanilla, I get the message "cannot open [wadname].wad" before the "This version of Doom has been modified" message. The full episode 1 replacement I made works, but when I tried taking out all of the maps but one, it wouldn't work. I even tried putting empty map markers for the other levels, but no luck.

[Scet]

That error should only occur if Doom can't create the file handle. Is the WAD open in another program?

This is the code that produces the error:

    if ( (handle = fopen (filename,"rb")) == NULL)
    {
	printf (" couldn't open %s\n",filename);
	return;
    }

[DuckReconMajor]

Got it. Filename was too long. Thanks!