We have experienced this in our organization, too.  It is related to the folder depth.  We only find this problem occurring when a user attempts to "Open with Windows Explorer" from more than two folders beneath a Document Library.  Unfortunately, I cannot explain why this would be the case, but at least it seems to be consistent and repeatable.

You will find a useful whitepaper on fixing Explorer View if you Google "Understanding and Troubleshooting SharePoint Explorer View" (with the quotation marks).

Hello,

I am experiencing the same behaviour.

The first level of a document library cannot be opened with Windows Explorer, but once I go into a folder it works fine.

I already looked at the post that Nadeem proposed but it didn't solved the issue.

Hi

A work around for this is to switch to explorer view in the library level itself . Then navigate thro the sub folders

Windows Client Service needs to be active in that particular client machine. To know more on the protocol used for explorer view , please refer to the white paper from MicroSoft

www.microsoft.com/.../details.aspx

You need to unzip this word document.