I have a client running Office 2007 and they cannot open .XLSX files by dbl-clicking on them. When I double click the file, I get the "openning rotating circle" for a moment and then nothing happens. The files DO open correctly if they first open Excel and then browse to the files to open them. Their Office 2007 has all the available updates installed, including the Compatibility Pack SP3. They are running Win7 Pro with all the updates installed. Any thoughts on what is causing this?

Thanks for any suggestions.