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Q129773: Error Message: LPT<n>: Windows Cannot Write to This File

Article: Q129773
Product(s): Windows for Workgroups and Windows NT Networking Issues
Version(s): 3.11,3.5
Operating System(s): 
Keyword(s): msnets
Last Modified: 19-MAR-2002

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The information in this article applies to:

- Microsoft Windows for Workgroups 
- Microsoft TCP/IP-32 for Windows for Workgroups, version 3.11 
- Microsoft Windows NT Workstation version 3.5 
- Microsoft Windows NT Server version 3.5 
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This article contains information about using Windows for Workgroups
version 3.11 with third-party products or configurations that have not
been tested and are not supported by Microsoft.

If the steps in this article do not function properly, use a supported
configuration or contact the manufacturer of your third-party product for
more information.


SYMPTOMS
========

When you try to print to a shared printer from a Windows-based program such as
Microsoft Word for Windows or Microsoft Excel, you receive the following error
message:

  LPT<n>: Windows cannot write to this file. The disk may be full. Delete
  any unwanted files and try again.

CAUSE
=====

This problem can occur when you print from a computer running Windows for
Workgroups 3.11 using Microsoft TCP/IP-32 3.11a to a shared printer on a Windows
NT Server or Workstation 3.5 computer using Microsoft TCP/IP, and the print job
goes through a "black hole" router before reaching the printer.

A black hole router does not return an Internet Control Message Protocol (ICMP)
"destination unreachable" message when it needs to fragment a packet that has
the Don't Fragment bit enabled.

RESOLUTION
==========

To correct this problem, follow these steps:

1. Add the following parameter to the Windows NT registry:

  ENABLEPMTUBHDETECT=1

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

2. Use any text editor (such as Notepad) to edit the SYSTEM.INI file on the
  Windows for Workgroups computer. Add the following line to the [MSTCP]
  section of the SYSTEM.INI file:

  PMTUBLACKHOLEDETECT=1

MORE INFORMATION
================

The PMTUBLACKHOLEDETECT setting is the Microsoft TCP/IP-32 equivalent to the
EnablePMTUBHDetect setting. Setting the EnablePMTUBHDetect setting to 1 (true)
causes TCP to try to detect black hole routers while performing MTU discovery. A
black hole router does not return an ICMP "destination unreachable" message when
it needs to fragment a TCP packet with the Don't Fragment bit set. TCP depends
on receiving these message to perform MTU discovery. With this setting enabled,
TCP tries to send segments without the Don't Fragment bit set if several
retransmissions of a segment go unacknowledged. If the segment is acknowledged
as a result, the MSS is decreased and the Don't Fragment bit is set in future
packets on the connection. Enabling black hole router detection increases the
maximum number of retransmissions performed for a given segment.

REFERENCES
==========

For additional information about adding registry values in Windows NT, see the
online Help file for Registry Editor, or see the following article in the
Microsoft Knowledge Base:

  Q120642 TCP/IP and NBT Configuration Parameters for Windows 2000 or Windows
  NT


Additional query words: prodnt 3.11

======================================================================
Keywords          : msnets 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNT350search kbWinNTW350 kbWinNTW350search kbWinNTSsearch kbWinNTS350 kbWinNTS350search kbAudDeveloper kbTCPIPSearch kbWFWSearch kbZNotKeyword3 kbTCPIP311
Version           : :3.11,3.5

=============================================================================

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