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"Open in Windows Explorer" Mode Not Working in WSS 3.0

By hagrin - Posted on 05 June 2012

Short version - Check to see if you have URLScan installed on your SharePoint server and, if so, uninstall it using Add/Remove Programs from the Control Panel.

At work we have a Windows SharePoint Services 3.0 setup that usually runs pretty well without any issues. However, seemingly out of nowhere, a user discovered that the "Open in Windows Explorer" option on every list had stopped working. We hadn't done any updates recently, no changes to the server were made, but since our site isn't used that frequently (especially that functionality), there was no way I could narrow down exactly when this functionality stopped working. Here is a rundown of what we encountered with this problem -

  • Windows SharePoint Services (WSS) v3.0 (SP2)
  • Windows Server 2003 running IIS 6.0
  • "Open in Windows Explorer" does not work. On a client machine, you would experience either 3 authentication challenges, never-ending challenges or, on the server itself, just nothing would happen - no explorer window would open, no challenges, nothing.
  • Account used to attempt logins was a Domain Admin with basically full access to every network resource.
  • No actual error messages displayed.

So, there wasn't much to go on. I tried a whole bunch of troubleshooting steps that I found while searching Google and nothing worked. However, I started to understand that the entire process revolves around WebDAV - something that I really didn't have too much firsthand experience troubleshooting. After a very, very long time and having to manage all of our SharePoint sites manually, I finally caved and called Microsoft support.

For about a week, a few hours per day, the tech walked me through a lot of the same steps I had already tried. We tried disabling WebDAV in IIS since that could potentially interfere with the "Open in Windows Explorer" functionality. We looked at setting some registry keys controlling authentication and we tried changing settings through the Central Administration site and the Alternate Access Mappings there. None of these troubleshooting steps worked.

At this point, I was required to run NetMon 3.4 on both the server and a workstation and acquire a network capture on both machines. This was the key to unlocking what the cause of my problems were. After looking at the captures, it was evident that something was blocking the WebDAV requests resulting in HTTP 404 errors. At this point, the Microsoft tech asked me if we had Microsoft URLScan Filter installed. I honestly had no recollection of installing it and no documentation stating as much, but low and behold there was a shortcut on my server's desktop to a URL Scan folder containing logs starting over three years ago!.

So, the solution was easy - Just uninstall URLScan from your SharePoint server! It seems that, in some instances at least, that URLScan blocks certain WebDAV communication. Hopefully, uninstalling URLScan fixes your SharePoint WebDAV Windows Explorer issues as well!

PS - Of course, once I knew the solution, I was able to find this post that basically outlines the fix posted over 7 months ago. Sigh.