Interrupts 101

[matador29b]

Hello everyone. I am having a bit of a problem, this code (or it's equivalent) works merrily on assembler, but it seems to lose the declarations for the ports after if executes the interrupt routine.
Can anyone tell me what I am doing wrong? This code works ok, but as soon as it hits the asm routine, it stops working. The interrupt works, the sequence works, values are sent to the variable portc.3 but the port does not respond. Even if I use "portc.3" instead for led4, it does not respond.

Thanks for your help

(at 4Mhz, there would be 234375 interrupts per minute, roughly 1500 interrupts per half a second)