Error Msg "Cannot sort a range containing merges." in Google Sheets

Using Google Sheets. Why am I getting this error msg? "Cannot sort a range containing merges." I DON'T have any merged columns, or merged anything. No hidden columns, or at least they weren't hidden when I tried to do the sort.

I tried to attach the file as a XLSX, and CSV, and both formats gave me an error.

Thanks A Guy (BTW, like the moniker), I fixed the issue. The problem was that I wasn't aware that the last column on the right was merged with all of the columns to the right of that. Unmerged, and fixed it.

Thanks,
GPLea