Parsing error - help please!

Have posted this also in Mentor forum - but am posting here also in the hope that premium members forum might get a faster response..

I have subscribed to diamond subs in order to use Mentor; I'm getting same error ("An error occurred during Ajax response parsing") when trying the first Mentor ROE023 King & Rook vs 2 disconnected pawns on a mac running latest versions of OSX, Safari, Firefox, Chrome etc. I've updated Java and Flash, allowed pop-up windows and restarted the mac/cleared all cookies and temp files. Nothing works.

I'm on a broadband connection with no downtime issues. What can I try next to solve this please?

How long is that one window open before you do anything on it when the ajax error appears?

Strangely it just started to work today - and I can't think what I did differently; though am also following advice given to me in another forum: http://www.chess.com/forum/view/chess-mentor/repeated-run-time-errors?page=2.

One thing I found, without even realising how much time passed is that I leave the chess mentor page open. When I then try to use it, I sometimes get the same type of error, but if I refresh the page first, it doesn't happen. So its like I've left the page open too long without doing anything on it. If it happens again for you, can you try to remember how long the window was open before you did anything on there or how long it was open before the error appears? 

In fact I had the problem from the get go: ie from the very first time I started to open and use Mentor, having just subscribed to premium plan. It's bizarre that now it works absolutely fine on both my macs - I'm beginning to wonder if it was some kind of connection or server issue...

I have the very same problem with firefox. No matter what I try, I always get the error "error during AJAX response parsing".