The "Unexpected File Format" error occurs when something has corrupted the Timeless Time & Expense Single-user (*.tls) file.  Historically, this has been disk corruption and not related to the operation of Timeless Time & Expense.

The corruption can occur when saving the file saving the *.tls file if it hits a "bad" part of the harddrive.  The file may also become corrupted after the file is saved.  If the corruption occurs during the save and the operating system reports it, there will be a backup file.  Depending on the version of Windows and the original file location, the backup will be found in different places.  Use the Windows search functionality to search the entire drive for "<filename>.tls backup" where <filename> is the original file name.  If the file is found, open it to verify its contents.  If the file is acceptable, copy it to the original filename and open it in TT&E.

If you do not find the file, restore from a previous backup using your Backup software.