DOCUMENT:Q129773 19-MAR-2002 [crossnet] TITLE :Error Message: LPT: Windows Cannot Write to This File PRODUCT :Windows for Workgroups and Windows NT Networking Issues PROD/VER::3.11,3.5 OPER/SYS: KEYWORDS:msnets ====================================================================== ------------------------------------------------------------------------------- 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 ------------------------------------------------------------------------------- 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: 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 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2002.