corrupt xlf file?

I have a xlf file (originally converted from 4.5) that used to open just fine. However, I now get an error message saying "problem accessing Excel, exiting" and Xcelsius just shuts down and I can no longer open this file.

Since the excel file is embedded I can't even open that.

Help - I have made a lot of changes to this file - how can I stop this error and open the file once again?