I should not have much trouble using MPASM. I just tried it with the present version of my program, and it works well. It only reported that strange error when there was the n-bit math code present.
Without that code, it assembles my program well, but still reports over 200 messages about crossing page boundaries. I hope these messages can be disabled somehow, because they make any real error messages scroll out of the window AND out of the screen buffer!

I guess that with enough time, things will fall into place.