Your server administrator has limited the number of items you can open simultaneously

Users are getting te following msg:

Your server administrator has limited the number of items you can open simultaneously. Try closing messages you have opened or removing attachments and images from unsent messages you are composing

and in exchange events I see : MAPI session (user) exceeded the maximum of 250 objects of type "objmessage".

I found this

https://www-secure.symantec.com/connect/forums/you...

but the links are broken and they are saying that there is a fix for 9.0.1.

We have version 10.0.4 (clean installation, not upgrade)

Any ideas?

Sarah