Agreed it won't look good to 'force' them but perhaps you can gently persuade them that they need to update to 6.52 as it fixed various bugs including the problem with getting files from v7, exported to 6, in!
Honestly, that will be, I suspect, the only route. My experience of trying to get anything below 6.52 to open a saved down v7 file has been a total disaster.
Greg
I think therefore I am, you're pink therefore you're spam