You have opened two instances of the Approval Templates — Setup window and displayed in both of them the same approval template in which there is only one originator

You have removed from one of the instances the user that is listed in the Originator tab, and then tried to remove it also from the Originator tab of the other instance

In both instances of the Approval Templates — Setup window, choose Cancel

Open the Approval Templates — Setup window once and remove the originator