The evt_nam_TUR_Mustafa4_Sultan1807 event looks simply and straightforward enough, and I can't see an error in it. The only unit it should remove is 'Sultan Selim III' (ldr_TUR_Selim4).
But looking at the <F1> unit list one can see that the only Turk unit in the game is 'Sultan Mustafa IV'.
I would guess there was a glitch while executing the turn, and suggest re-running it. Also, the logs from right after running the turn (before starting the game again) might shed some light on the situation.