6.9.3 sessions in PT 7.1
 

Dear Friends,
We've recently upgraded one of our PT from 6.9.3 to 7.1. But we're having problems to work with our old 6.9.3 sessions in PT 7.1. The problem is that, when we open it, PT 7.1 becomes slow and the transport window doesn't accept any commands anymore - neither by mouse clicks nor keystrokes.
This is the same if we open the 6.9.3 session in PT 7.1, save it in 7.1 format, and reopen it as a 7.1 session in PT 7.1. This process would represent converting the session from 6.9.3 to 7.1, isn't it?
My question is: Is 6.9.3 session full compatible with PT 7.1? Or is there some special procedure to convert it and/or use it in PT 7.1?

Best Regards.