I faced this error very long and my solution ended with below tweak.
This is solution which also works for Exchange 2010.
Simply open registry editor.
Locate folowing reg entry
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
create Dword-32bit entry.
"Maximum Allowed Sessions Per User" to some decimal value
Restart Microsoft Exchnage Information Store service.
This is solution which also works for Exchange 2010.
Simply open registry editor.
Locate folowing reg entry
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
create Dword-32bit entry.
"Maximum Allowed Sessions Per User" to some decimal value
Restart Microsoft Exchnage Information Store service.