Bruce,

jumping around the SERIN2 statement has the same effect as commenting it out.
(It will not be executed)

and all available ports are blinking LEDs on and off nicely.
(Even with the RF transmitters antenna bound around the 18F)
(I can't produce much more RF noise on the 18F, can I)

It is SERIN2 that is causing a problem on the 18F, not RF or any other noise.

This is probably the time to start a new thread: "18F252 SERIN2 problems"