Make sure you are protecting all the registers you are using in both interrupt routines.

For example, if you are using the accumulator, be sure to PUSH ACC at the beginning of your routine and POP ACC at the end of it. Otherwise, the two interrupts are going to be overwriting each other's registers--and both interrupts will be overwriting registers used by the "main" program. Also don't forget to analyze whether you need to protect PSW, as a number of instructions will modify bits in PSW even though your program doesn't explicitly modify it.

Also be sure to check that you are, in fact, using RETI to terminate both interrupts.

You may want to use a Simulator that informs you of common interrupt errors. There are a number of simulators that include such warnings.

If you aren't writing in assembly language, please ignore this message as it probably isn't relevant.

Take care,
Craig Steiner