I too use the Metalink assembler.

Your problem may only be the assembler directive that specifies what model of microprocessor your are using.

For example, the system I write for does not have a Port 5. If I include a statement directing P5, I'll get a assembly error.

I have two ways of correcting this. First I could examine the list of models that my copy of Metalink supports. I'm sure someone will tell you where to find updated models (maybe a new topic would get their attention). You could copy an existing model file and hack it. (just open the model files and find one including a P5 and you'll probably be able to assemble your code.)

I used a different approach. I wrote my own header file for the microprocessor that I'm using and gave it the names I wanted to use.