If you have any non-date cells in that range--including empty cells or text
cells, you'll get this error.

And is there any chance that your pivottable uses too many rows--maybe you
included empty cells at the bottom of the data?

wrote:

Keep getting a "Cannot group that selection" when trying to group dates
by month in a pivot table. Dates are formatted correctly in the data
table.

Any ideas?

--

Dave Peterson