Rename virtual directory on Windows Server 2008 (IIS7 )

From the MSDN, your directory path should read: %windows%\Microsoft.NET\Framework\version\ASP.NETClientFiles\Themes.

MSDN on themes. Of course, there are caveats with this and it appears that your directory could work if certain circumstances are true.

If that isn't the issue, I would also verify the permissions on your Themes directory. The ASP.NET worker process and IUSER or whatever account is running your website will need read access as well to all folders and subfolders of your theme. Are you getting any runtime errors with your setup?

When using a virtual directory that's pointed to a UNC share, go to advanced settings for the virtual directory, then choose a specific user account that has the appropriate rights to access the folder. It works for my virtual directory in my asp.net app that is pointed to a UNC share on a remote server.