Suddenly I'm getting the following error when I try to double-click on an
Excel spreadsheet to open it:

Windows cannot find 'xxxx'.  Make sure you typed the name correctly, and
then try again.

"xxxx" is the full path and filename of the document I'm trying to open.

Additionally, it seems that double-clicking a spreadsheet opens a second
instance of Excel instead of using the currently open instance.  I have no
problem dragging a spreadsheet into Excel or opening a sheet from within
Excel.

Any help would be appreciated.

Thanks,
Robert