Select the entire range to sort.
format|Cells|alignment tab

Is that checkbox for merge empty?

If no, then you have some merged cells in that range.

jpas1954 wrote:

I'm trying to sort a column (and adjacent columns) and keep getting this
error. I'm not clear on what it's trying to say or how to resolve it. I don't
have any merged cells:

This operation requires the merged cells to be identically sized. This error
only appears if you attempted to sort a range of previously merged cells, but
not all cells in the sort range were merged or are not of the same size.
To avoid this behavior, unmerge all the merged cells in the range, or merge
all the cells in the range to be the same as the largest merged cell grouping.

--

Dave Peterson