Hi Angus,
Considering all MPASM errors are assembly errors, and IF they correctly worked in PBP 2.5 my best advice is to look carefully at your config settings. Try deleting the config in your code and see if it compiles with success. Otherwise I would need to SEE your code. PBP issues will report, likely in red . . .
Many times errors report as xxx.asm with a line number. you can open the yourfilename.ASM page and scroll to that line number.