I'm running Excel 2003 and Windows 7 x64. Lately, clicking on an XLS file name in Explorer or from a desktop shortcut brings up a blank worksheet in Excel, plus an error message with the filename and path in the header and "There was a problem sending the command to the program."

I can still load these files by clicking on them in the File/Open command in Excel, or inthe list of recently used files.

How can I fix this?