I cannot open the .xla file with Excel 2010. When I double click the .xla file, I first got asked whether I want to enable macro, which is expected and I answer yes, but then this error message appears: "Invalid procedure call or argument" which I click OK on. After this the Add-in tab does not show up at the top of the screen although I can still click on Developer->Visual Basic to view the code of the add-in.
I used to use Excel 2003 and recently changed to 2010 and everything had been running fine until today, The QA guy who is accessing the same .xla file uses Excel 2003. He might have done something, but I am not sure.