HELP! Error message, can't open Company.

I closed Sage and now when I open it I get the following error message.  I didn't do anything different than I normally do.  How do I fix this?

"Can not open company file .... This data has been updated to a new file format and is not compatible with this version of the software"

Any ideas?  I didn't change or update anything.  I just backed up as usual and closed the company.  When I went to reopen this happened.