Nick Stahl has been arrested for allegedly committing a ''lewd act'' at a porn shop in Los Angeles.The troubled 'Terminator 3: Rise of the Machines' actor was arrested by Los Angeles Police Department undercover vice officers at the store after they allegedly discovered him ''touching himself'' in a private booth, according to gossip website TMZ. However, Nick, 33, insisted the whole incident was a ''misunderstanding''. This is the latest in a string of setbacks for the actor who was reported missing in May and again in June. After his fist disappearance he re-emerged and was admitted to a rehabilitation clinic. However, he walked out of the facility and went to stay with a pal but was again reported missing when he failed to return to the friend's home. A source said at the time: ''Now he's disappeared. We can't find him anywhere. He has not made contact with anyone. We are all just desperately looking for him. ''Everyone just wants him to come home. It's a terrible situation. We are searching, but we've had no solid leads.'' He is estranged from wife Rose Murphy Stahl with whom he has a two-year-old daughter Marlo.