We've been configuring Service Desk and experienced the following scenario.
We have an approval workflow, which is set so that when ticket is created is giong directly to status Under Approval (no open status). Aditionally, on the create transition, we have set that instead of Issue Created, Generic Event is called. This is set in order not to send Issue Created notifications since the ticket needs to be approved first.
Now, whenever the reporter and approver are the same person, the request cannot be approved. The attached error appears.