If you receive the following error in Exchange 2010 it can be resolved by upping the MAPI session limit in the registry.
MapiExceptionSessionLimit: Unable to open message store. (hr=0x80040112, ec=1246)
To set the Maximum Allowed Sessions Per User:
- Start Registry Editor.
Locate, and then click to select the following registry subkey: <pre>HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem</pre>
- If the Maximum Allowed Sessions Per User does not exist, do the following:
- On the Edit menu, point to New, and then select DWORD Value.
- Type Maximum Allowed Sessions Per User as the entry names, and then press Enter
- Right-click Maximum Allowed Sessions Per User , and then click Modify.
- Click Decimal, type the value that you want to set in the Value data box, and then click OK.
- Close the Registry Editor.
Restart the Information Store Service:
sc stop MSExchangeIS sc start MSExchangeIS