Sharepoint - Unable to open office files in Office client

I noticed that SharePoint Worksapce was running in the system tray which had the "Shared Documents" library synced, because of this there were some temp files out there in the following location

"c:\Users\login_user_name\AppData\Local\Microsoft\Office\14.0\OfficeFileCache"

after terminating the Sharepoint workspace and clearing those temp files, I was able to open documents in Office client.

You can simply close all office application and navigate to the location above, shift del all files and try to access the files again, it worked like a charm for me

We had to open a case with Microsoft about this same issue. We literally tried every solution suggested in this thread and many others (IE settings, Office Trust Center settings, removing cache directories, etc, etc). It turned out that a pre-release version of Office was installed on the affected machines. The pre-release version (found in Control Panel -> Programs) was 14.0.4734.1000. Microsoft support told us that the pre-release version had issues integrating with SharePoint. Uninstalling the pre-release version and installing a release version solved it for us. I hope this prevents some weary soul from investing the hours we did into a bunch of nothing!!!

Here's the link for valid release versions of Office:

http://support.microsoft.com/kb/2121559

The only thing I can think of is that when opening a file from SharePoint directly, Word uses WebDAV to communicate with the server. If this protocol is disabled in the firewall for instance, Word would be unable to retrieve the contents of the file.