Not really an issue or at least it shouldn’t be, if something is generating more than 50 concurrent NSPI connections, it likely needs to be checked out anyway…
NSPI connections from Microsoft Outlook to a Windows Server 2008-based domain controller may fail with an error code: “MAPI_E_LOGON_FAILED”
This behavior occurs because Windows Server 2008 only allows for a default maximum of 50 concurrent NSPI connections per user to any domain controller. Additional NSPI connections are rejected with a MAPI_E_LOGON_FAILED error code.
See the whole support KB here —> http://support.microsoft.com/kb/949469