You'll have to look thru' the .db files as I had mentioned on the previous page...Check if there's anything you can modify to solve this issue...

AFAIK, the n9 is not made for a huge number of messages...Anything above 2k slows down the phone; try plugging in your phone to Nokia Suite and a warning will come about this figure...

Anyway it still should be fixable...Just look thru your .db files...