I would STRONGLY suggest re-compiling all the source codes with your most recent tool set and linking with the new linker. The previous comments about calling convention differences are SO true and you could spend DAYS debugging a mess that looked like it linked ok.

I would not even trust object files from an early 90's vintage compiler from Avocet against the object files from a current vintage tool set from the same vendor unless they were emphatic via their customer support line that the object formats and calling conventions were 100% compatible.

The biggest issue is the calling conventions by far. Compiler vendors have made huge strides in the last 15 years at the quality of compilers and how they optimize and perform calles between routines.