If you have that message onscreen, but you can still use the terminals, just keep rolling. The trans.log may have some errors that make for problems generating reports, but finish the day and worry about that later. There's a flag in store settings (continue FOH on log error) that's obviously checked in your case; this is the situation it's designed for.
And any time anybody tells you to rename/move/delete the log in the DATA folder, start looking for help elsewhere. That's not for a user, that's the kind of thing you only want done by trained support.
Case in point: there's plenty you can do to fix the log, especially in a case like this. Once EOD runs, you can run grind/grindq with the /fixlog flag to take care of most corruption. You may have a fixlog program somewhere on your BOH machine that you could run, but note that these are version-dependent. Also, if you had removed or renamed the log and started a new one, you can rename the second log, merge them with a DOS command (copy /b old.log+new.log merged.log) and rename the result to trans.log, put it in the dated subfolder, and regrind. You may need the /fixlog grind/grindq flag or the fixlog.exe for your version after that.