Could be anything from Win 8 specific issues to the usual flattening problems with EPS. nobody can say without seeing your artwork...
It was a Windows 8 issue. I took my .ai file to work (Windows 7) and it saved as an EPS with no problem. Thanks. I should of purchased a Mac.
I don't think it is a Win8 issue per se. I export to EPS from both CS5.1 and CS6 on Windows 8 64-bit. It may well be a user account issue or the CS6 installation itself.
Try creating a new user account on the Win 8 computer and try it. Only takes a few minutes with the reboot.