Windows 2008 changed the NSPI from unlimited to 50 connections. This can affect a number of applications including Symantec , Blackberry , and others.

The real issue involves 3rd party (non-Microsoft) products (again, like Symantec & Blackberry) .
While Symantec may recommend setting this value to 0xffffffff (~4 billion) effectively rolling back this setting (to be fair, they do state it may not be desirable to set the max limit and provide a formula). I would not recommend setting NSPI to such a high value. Set it to 100 or 150 to see if that resolves the issue first. Then gradually increase the number by about 100.
The real issue is the application needs to be tweaked to handle the connection limit.

From Microsoft KB 949469:
To resolve this issue, check all NSPI connections that processes on the client create for connection leaks. For example, a call to the NspiBind function must have a corresponding call to the NspiUnbind function when an NSPI connection is no longer required. This operation may require that you debug any custom scripts or applications that are using NSPI. If this issue affects external applications, contact the software vendors for updates.

Note The Outlook NSPI MAPI provider that is installed with Microsoft Outlook is only intended for use with Microsoft Outlook. External scripts and applications that rely on the Outlook NSPI MAPI provider are not supported.

References:

• How to troubleshoot connectivity issues that are caused by RPC client protocol registry entries
• NSPI connections to a Windows 2008-based domain controller may cause MAPI client applications to fail with an error code: “MAPI_E_LOGON_FAILED”
• Raising Your NSPI Connection Limit
• Admin Tips: Windows Server 2008 Changes in BlackBerry Environments