I pasted a range of cells from a results sheet to a graph in Prism. Now I can't reformat the pasted table to change the range. What's wrong?

This is a bug. After double-clicking on the pasted table to access the "Format [Embedded] Table" dialog, you cannot change the setting of "Include Y values from..." to include date sets beyond the Z column.

It's easy to work around the problem. Just erase the table, then paste the new range to make a new table.