Many time this is just graphic and the cutter should not be going down in a gap you see.
make sure you and your co-worker are picking the model the same way to machine. sometimes when you pick only certian surfaces or solidfaces this could happen. I just made a how make and fix surface cd on my site that may be of interest.
http://www.cad2cam.net/mastercamx_basic_surface%20.html
If you could share your part this may help.
Steve
www.cad2cam.net