Hello.
We're having an issue in our environment in which outside Excel 2010 users cannot open .xls files that have been opened/modified by Excel 2013 users. The file format is kept exactly the same and prior to the upgrade to 2013, those same 2010 users could open the files just fine.
When the 2010 users try to open these files, they get error messages about the file being corrupted.
We have found a temporary fix. If the 2013 user saves the file as an .xlsx file, then the 2010 user can open it just fine. This is a pain though as we'd have to convert every single .xls on the network.
Has anyone else seen this issue?