PLT file not transfering to cnc

I am wondering if the coding was changed from X3 to X7 when saving as a .plt. I use the .plt files to post to an older CNC router, and after upgrading to X7, the .plt files cannot be read by the cnc software.  Has anyone had issues with .plt files? I downloaded a trial version of X6 and it worked, so the change had to occur between version X6 and X7. I wish I would have purchased seats of X6. Now I am over 30 days and Corel wants to charge for every support call. I guess I shouldn't have assumed it was ok.

The X7 program loaded ok and the students have been designing. However, now they need to output the drawings, and I am having problems. 

Any help would be appreciated.