Wed May 30 17:39:07 EDT 2012

Electrical problem?

Reading the 18F2550 datasheet, here's something I missed: Internal Regulator

  The PIC18FX455/X550 devices have a built-in 3.3V reg- ulator to
  provide power to the internal transceiver and provide a source for
  the internal/external pull-ups. An external 220 nF (±20%) capacitor
  is required for stability.

I found it looking up "VREGEN" from inspecting the configuration bits
in piklab.

EDIT: Adding the 220nF did the trick.

Another one for later:

  The data in the USB Status register is valid only when the TRNIF
  interrupt flag is asserted.