Error opening some files in coreldraw x6

I get this error only in coreldraw x6 in coreldraw x7 (trial)  I can open the files without any trouble.

If I open the file in x7 and save it as x6  -> i now can open it in coreldraw x6.

It's with several files this error occurs:  old ones (created in x4) , new files ( created in x6)...

file size doesn't matter , it happens with small files and also with larger files.

We have 5 licenses of Coreldraw x6, 2 pc are having trouble opening files ( both windows 8.1 pro x64 version) the others are windows 7 x86.

all patches and hotfixes are applied.

Tried increasing virtual memory , reinstalling , resetting workspace, cleaning temp folders, ...