[Mark McLeod]

It has all the symptoms of running out of data or program space.
Sorry to say (or is it good news?) there's absolutely nothing wrong with the code you posted (as you knew). The only thing you didn't mention is how much data space you are filling.
A simple test would be to comment out something else that frees up data space, then add in your abs function.
Any overly large arrays hidden elsewhere in the code, array macros used repeatedly (found one guy who did that with his SIN table, boy did his data space disappear fast!), other things that don't show up in the program space total?

Try varying the combinations of other software you've added in with particular attention to high volume variable users.

If you'd like to email be your zipped project I'd be glad to serve as a second pair of eyes. You know how it can be sometimes when you're looking at your own code.

[edit]
As a side note I just noticed today's revision of the FRC default code removes some IFI debug code and frees up more program space.
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