InCopy changing files between computers

I need some help with InCopy. We work with InC and InD. On my Mac, I can open an InD file, edit it, do copy fitting, etc. Once I check-in all, save and close the INDD, I can reopen it on my computer and it will appear just as I left it. However, when an associate opens the same file on their Mac the copy will be overset. Are we having a font challenge? Is there some other issue at play? Thanks for the assistance.