Blue Screen in Win XP SP3 when changing folders or renaming folders - SOLVED

I had the bad experience with the MyBook World Edition that it would blue screen whenever I changed folders or tried to rename a folder.  It did not occur with other computers and Macs.  Here was what I did to resolve this ANNOYANCE:


  1. Purchased new WD My Book World Edition ‘Network Attached Storage’ for home to permit transcription of old reel-to-reel tapes to CD.

  2. Every time I tried to create or rename a folder on the NAS, got  a blue screen with error  


  1. Ouch.  Thought the NAS was broken.  However, error did not occur on other XP workstations or at all on Macs (of course).  Assumed Mac was OK.

  2. Research revealed that the culprit is MUP.SYS, which is the dohickey that supports "Mup.sys This is the driver for the Multiple UNC Provider, which determines which network client protocol to use when the target server is specified by a UNC path such as \Server_Name. / Boswells Q&A Mup.sys is the service to connect to Novell servers. "  And it also apparently is the key dohickey for talking to a NAS like this one.

  3. My version of MUP.SYS was OLD.  Even though it supposedly was replaced by XP SP3, that really did not happen. Hence, I renamed the MUP.SYS in C:\WINDOWS\SYSTEM32\DRIVERS to MUP.SYSZ first, then copied in the new version from SP3 leftovers per the instructions).  (See also

  4. The configuration fix was:


File information
The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.
Collapse this tableExpand this table
File name    File version    File size    Date    Time    Platform
Mup.sys    5.1.2600.2763    105,088    23-Sep-2005    01:26    x86

Registry information
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756  ( ) How to back up and restore the registry in Windows

After you install this hotfix or a service pack that fixes this issue, modify the DfsIrpStackSize registry entry. To do this, follow these steps:

  1. Click Start, click Run, type regedit, and then click OK.
  2. Locate and then click the following registry subkey:
  3. In the right pane, right-click DfsIrpStackSize, and then click Modify.

Note If the DfsIrpStackSize registry entry does not exist, you must create it. To do this, follow these steps:
a. On the Edit menu, point to New, and then click DWORD Value.
b. Type DfsIrpStackSize, and then press ENTER.
4. In the Base box, click Decimal, type 10 in the Value data box, and then click OK.

A value of 10 allows for a maximum of eight file system filter drivers.
The default value of the DfsIrpStackSize registry entry is 5. A value of 5 allows for a maximum of three file system filter drivers.
If you set the value to a number that is greater than 10, the value is automatically set back to 5.
If you do not apply this hotfix, the DfsIrpStackSize registry value is ignored.
5. Exit Registry Editor.
6. Restart the computer.

  1. Did all this, now works fine AFAICT

  2. However, a hidden benefit, or perhaps  a perceived benefit, is that network queries and login/startup are noticeably faster.  Might be that MUP.SYS was a throttle on performance.

Over and out.

MyBook World Edition 1TB with white lights