We have a server to server integration from our Calendar application and MS Exchange Server. The integration is based on MAPI with CDO extension. To capture changes that occur in Exchange server, we use the Event Notifications as Exchange Server provides. When a user’s calendar is changed we get event notification that a change has occurred. To subscribe to the changes from the Exchange Server we need for each calendar user to create a connection(mapi session) to the Exchange server and register notifications from Exchange Server using IMAPIAdviseSink. That part used to synchronize the calendar changes from Exchange Server into our application. We store the calendar information in our application. We have now some problems reported from our customers who upgrading to Exchange Server 2007. The problem is that when we register all application users – employees for our customers – to receive notifications from Exchange Server 2007, we get a logon error in MAPI when we try to create a MAPI connection with user no.33 and the other users after hat user. The error we get is:"The information store could not be opened. [MAPI 1.0 - [MAPI_E_LOGON_FAILED (80040111)]] " After some investigation, we find out that it’s a limitation on the number of open MAPI sessions from a user on Exchange Server 2003 SP1 an newer versions:"Exchange Server 2003 SP1 impose a restriction on the number of permitted MAPI sessions per user. By default, the maximum number of permitted MAPI sessions per user is set to a hexadecimal value of 0x20 after you apply Exchange Server 2003 SP1. "[Ref: http://support.microsoft.com/kb/842022] We have tried to follow the solution suggested in KB842022 without that we have succeeded to solve our problem with the number of open sessions. For the user, we added the access right: “Vies Information Store Status” (Could not do that from Exchange Management Console” since the Security tab does not exist): [PS] C: \ Windows \ System32> Add-ADPermission-Identity "Seref Boyars" ExtendedRights "View Information Store Status" We have changed following registry subkey on Exchange Server: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem Maximum Allowed Sessions Per User til 100 (decimal) We have restarted the Microsoft Exchange Information Store, we have also restarted the Exchange Server computer.I have also disabled tcp shimney without that solved my problem. Afterwards, we restarted our application, and get same problem from user no. 33: "The information store could not be opened. [MAPI 1.0 - [MAPI_E_LOGON_FAILED (80040111)]] " I get the same problem in Outlook 2007 client if I try to open calendars for same users, I get error on calendar no. 33.Do you have any suggestions for any solution? We are grateful for any thread that may help us to solve this problem.