If a Windows NT 3.1 computer is sharing a printer that is redirected to a Windows NT 3.5 computer, downlevel clients (like MS-DOS or Windows for Workgroups) print jobs get stuck in the Windows NT 3.1 print queue.

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When a Windows NT 3.1 computer sends a downlevel print job, it sends the job as a null session. Null sessions are those where the user credentials are blank during the request to setup a session. Because the downlevel client may not have an account or because of a conflicting account on the second print server, downlevel jobs are sent as a null sessions. Security is up to the first computer in this scenario.

Windows NT version 3.1 supports null sessions by default. However, Windows NT version 3.5 does not provide this support unless specifically configured to do so. This change was made in order to provide a higher default level of security.

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This problem can be resolved by modifying the registry on the computer running Windows NT 3.5 to allow null sessions to the print share.

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

1.	Start Registry Editor and locate the following Registry subkey in the HKEY_LOCAL_MACHINE subtree: \SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters
2.	Select the NullSessionShares value.
3.	From the Edit menu, select Multi String. NOTE: values will already exist and should not be replaced. If the values are accidentally deleted, just click Cancel and try again.
4.	Select the first blank line after the values that currently exist. (The lines above should not be highlighted.) Add the name of the print share on Windows NT 3.5 you want to accept null sessions. This needs to be done for each share individually.
5.	Click OK and exit Registry Editor.
6.	Either shut down and restart Windows NT or from a command prompt type: NET STOP SERVER. Then type: NET START SERVER.

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For a Windows NT LPD server to support print jobs that are redirected to a second Windows NT shared print queue through a UNC name, NullSessionShares must be used. The UNC name of the printer share must be added as a null share on the second Windows NT print server. For example, if \\Server1 is the LPD server and it's port is redirected to \\Server2\Printer, the UNC name \\SERVER2\Printer must be added to NullSessionShares on \\Server2.

For additional information on using LPD, please see the following resource:

Windows NT Resource Kit 3.51 Volume 2, Networking Guide; Chapter 18, "Internetwork Printing with TCP/IP," page 357.

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