When I click on an Microsoft EXCEL file I have created in the past, Excel used to open and open the file. For the last two weeks Excel opens but fails to open the file and I have to use the file/open command. Have I changed an option or something?
Have you tried right clicking on the file, select 'open with ..' and then 'choose program' and highlight Microsoft Excel. At the bottom of the dialogue window there is a box that you can check to 'Always use the selected program to open this kind of file' and click OK .
If that doesn't work try the following link to the Microsoft KB