The only thing different from the stock version of OSTicket is the German translation pack. I've already tried turning it back to English to see if creating a new ticket works, but it didn't.
There was no official osTicket German translation pack back at 1.6.x - so I doubt you're the official osTicket 1.6.x and instead use a customized version from where-ever. And trust me, as German translator and proofreader I know that pretty good and 100% sure that there was no language pack for 1.6.x ;)Just out of curiosity (if you still know):Where did you download your 1.6.x version back at the days when you set it up?