Aberco,

Sorry, I deleted your modification because it was silly to use Timer0 for USB interrupts, and it won't detect Plugged, RX, or TX, that way.
Plus I don't want that code floating around.
Some Patience is required until I get settled. I don't have any computers or internet access at night right now.

I believe that all you need to do is change the USBIE and USBIF bits because Microchip moved them in the 13K50/14K50.
They used to be PIE2.5 and PIR2.5 in the 4550 family. Now they are PIE2.2 and PIR2.2 in those chips.

Please download the file again to start from scratch, then change to ...

Code:
USBIE              VAR PIE2.2        ; USB funnel Interrupt Enable
USBIF              VAR PIR2.2        ; USB Interrupt Flag