Hello,
just upgraded to Windows 7 and installed Office 2010. However, when I create Excel files then try to open them I get this message: not a valid Win32 application. If I open Excel first then do a FILE, OPEN, the file does open. What's up?
Your computer maybe is recognizing .xlsx files as executable files.
Right-click your file, go to "Open With" and "Choose default program". Then mark the "Always use the selected program to open this kind of file" and choose Excel. Then you're good