We had that issue also. Finally figured it out (at least in our shop). Basically, Corel 6 takes forever to write .eps files (and save .cdr also). Even when your monitor shows the file is saved or exporting, it is still writing. Try this. Export a .eps file and wait 10 -15 minutes and see I'd you can open it. Then export same file again (under different name) and try to open it right away. Probably can't.
Now my guys allow 5 to 10 minutes or longer after saving/exporting before using. We can quickly export files under Corel 4. Must be a bug in 6.