I knew I had seen this error message recently and after some digging, realized it was connected to this Flukebook post. Excel was doing something to the formatting that prevented it from being uploaded correctly.
I tested your spreadsheet as-is and was able to replicate the error. After a lot of testing, if you open your spreadsheet, “save as” without making any changes, and then upload the new version, it will accept it. I can’t figure out what specifically about it ACW doesn’t want to play nice with, but that at least seems to be the simplest workaround for whatever is going on with the original file.