you probably checked this, but if you leave the stock __config lines in the 18f4550.inc, the stock 20mhz config fuses will conflict with the specific 4mhz config fuses in USBDemo.bas.

I just fought with this ******* for like 10 hours, and it turned out to probably have been non-standard USB wire colors! I got frustrated, cut another cable with bizarre colors, and had to figure it out with a meter.. worked first time i hooked up that cable...

dont trust anything!
robert.