Recently, I came across the error below when attempting to open a large document library in Explorer View :

Some/SharePoint/Folder is not accessible.  You might not have permission to use this network resource. Contact that administrator of this server to find out if you have access permissions

Seeing as I am the administrator of the server, the site collection, the web application and the entire farm itself, I think I pass the permissions test.  It turns out that the real culprit has absolutely nothing to do permissions in any way.

The problem was that Explorer View uses WebDAV in order to populate itself and the document library I was viewing has over 20,000 items which resulted in a call to the server that returned almost 17 MB of data.  The default that is allowed for WebDAV in Windows XP and up is  1 MB and it is thus only processing part of the file which is now truncated and corrupted.  Broken Xml files are horribly bad things to work with so Windows throws up its hands with the error above.

The real SharePoint-ey fix is to do something utterly sane, like limit the number of items returned in the view to something that a normal human being can process, like a few hundred.  This would be well below the 1 MB limit and would display properly in Explorer View.

However, in my case, I needed one machine to be able to see ALL documents in that library in the folder, not merely a sampling of them.  The fix was to tell Windows to allow more data to come across for WebDAV.  This is a registry change so be sure to talk this over with your security admins and server admins first.

The TechNet article where I found this fix says it applies only to Windows XP but I experienced the same behavior in Windows 7 so it clearly has not changed.  Here is the important section from that article :

1. Click Start, click Run, type regedit, and then click OK.
   Locate and then click the following registry subkey:
2. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WebClient\Parameters\
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type FileAttributesLimitInBytesfor the name of the DWORD, and then press ENTER.
5. Right-click FileAttributesLimitInBytes, and then click Modify.
6. In the Value data box, type the value that you want to use, and then click OK. For example, if the Web folder contains 20,000 files, type 20000000 in the Value data box.
   Note If the default value is 1,000,000 (1 MB), Windows XP will enumerate a maximum of approximately 1,000 files in one folder. The actual maximum number of files may vary, depending on the number of file attributes or file properties. By default, the WebClient service does not ask for specific WebDAV properties. Therefore, the server returns all file attributes. The Microsoft Office integrated Webfolders redirector does ask for specific WebDAV properties.
7. Exit Registry Editor.
8. Stop and then restart the WebClient service. To do this, follow these steps:
   1. Click Start, click Run, type cmd, and then click OK.
   2. Type the following commands, and then press ENTER after each command:
      • net stop webclient
      • net start webclient

An easy way to see if this is the same problem you are hitting is to do the following steps:

1. Install and run Fiddler
2. Pause the capturing of requests by hitting F12
3. Navigate to the proper view in the document library
4. Start Fiddler’s capture again by hitting F12 again
5. Return to the browser and open Explorer View for the list

One of the first requests you will see will be the WebDAV PROPFIND request which is asking the server for the list of files.  If the size being returned is more than 1 MB then welcome to the club!