Trigger state on assignmend approval (on the same object)

Hi

I'm creating a workflow for the assignment class.

Now I'd like to transition a state when the assignment itselv is approved/finished, but the state transition-triggers only offer the possibility to trigger on a separate assignment approval.

I had the idea to use condition trigger when the approved-by property isn't empty, but this causes the error "Wrong parameter. (Duplicate user id.) (0x80070057)".

So is there another way to trigger a state transition when ON an object the assignment is approved?

(VBScript also welcome)

Thanks