Exchange 2010

Event ID 9646 is logged in the application event log of your Exchange Server 2003 computer when a client opens many MAPI sessions
http://support.microsoft.com/kb/842022

This should help increase the value to 32 ..... but if its for one user just check if there is some additional addons in Outlook that could possibly be causing the issue

- Rancy

Check this from social.technet.microsoft.com/

http://social.technet.microsoft.com/Forums/en-US/exchange2010/thread/91922b60-38b7-4af3-ba13-3b44949cc9f7/

R-R sir/ma'am are you really serious about what you've recommended? Does that mean if a single user has issues with multiple sessions open - you'd change that reg key and allow all users to have the new levels of sessions. Are you aware of the consequences of the performance hit on the CAS Server? I'm sure you'd have a better answer for my question - I'm monitoring this particular thread to read your response.

@zives2001: I'd check with the user and see what's wrong - have them shut their phones and see if the session error gets off, check and understand what the user is doing, sometimes users have the tendency to open upto 20-30 OL messages and they simply leave the machine idle - that leaves Exchange with no option but to have multiple sessions open. Educate the user to not perform such a practice.

You wouldn't believe how many issues get solved when we talk to end users and educate them.

Regards,
Exchange_Geek

@zives2011: Could you let me know what solved the issue? Also, did you investigate into what/why the issue was caused?

Understand that you've now allowed Exchange to allow sessions to a higher limit and that's the end of it. Next, time you hit this limit - no reg key would be able to solve this issue. Investigation would have solved it.

Regards,
Exchange_Geek