EMC to be used with MasterCam or ProE [asimtec]

Hi firends

Can some one tell me how do you use MasterCam or Pro-E to generate
programs that EMC can run without any problems?
Sometimes when i generate programs using MasterCam and run this
program in EMC in auto mode, the emc does some strange moves.
like x axis starts to travel in -ve direction till it touches the hard
limit. Sometimes the same program runs without any such problem.
Is there any such bug in EMC?

It would be very great help if someone could tell me what
postprocessor to use when generating tool paths from MasterCam or Pro-
E. Are their some unrecognized G or M codes which trouble with EMC?

Please share your experiences about how do you use EMC with MasterCam
or Pro-E?
regards

Asim