This means it thinks there are data/formulae/formatting in cells either at the very bottom of the sheet of the hard right edge AND, for some reason it thinks you're inserting a cell and trying to move cells below down, or cells to the right, right; do you have any macro code in the workbook at all?
No macros, but I did have some formatting (cell borders) that I had applied to blank cells on a couple columns. Once I removed the formatting, the error msg went away. It was funny; I just hadn't seen it before. It's weird that formatting would do that.