When I click on an Microsoft Excel .xls file, it says "There was a problem sending the command to the program"

Odd error: if I click on an Excel 2007 file to open it from within explorer, it says "There was a problem sending a command to the program". Excel opens - but it doesn't open the file. I have to then manually open the original file using Excel's "File..Open" dialogue.

All of my other Office 2007 apps work fine, including Word, etc.

Any ideas?

Answer

Fixed the problem by upgrading to Excel 2010. Initially I tried the 64-bit version, however, when none of my prior plugins loaded, I switched back to the 32-bit version which worked perfectly. Office 2010 is much nicer - it loads way faster.