These types of issues and post processor tweaking are best administered and handled with the assitance from your reseller (the company from whom you purchased ArtCAM).
Typically this type of an issue shouldnt be too complicated to adjust and fix but with that said it will all depend on exactly what isnt correct with the post processor and what your machine needs to read in order to run the code correctly.
The post processors in ArtCAM are controlled by a text file (.con) that can be edited by anyone who understands the G & M codes (providing that's what your machine needs to drive it).
The path to these text files (post processors) will be something along these lines;
C:\Program Files\ArtCAM Pro 9\Postp
If someone is not familar with editing these post and reading/understanding the codes then it is not advisable for these to be edited as it could cause major issues with your machine and how the code runs.
Again your ArtCAM reseller would probably be the best person to coordinate with in order to get this inverted issue resolved.
I hope this information assist you with how best to go about getting your problem resolved.