Problem with sh404SEF and JFBConnect

Hello Alzander,
I thank you very much for your kind words. You're doing a great job! After working two weeks on this problen, I still can not say what the error is, unfortunately.
I have found many entries on this topic but no solution.
Today I had an brilliant idea. I have sh404SEF replaced by MijoSEF(free Version). After a few small adjustments now everything works without problems.
I think the error has something to do with the language settings. In a Multilanguarge version I could solve the problem with sh404SEF. Unfortunately Jomsocial worked then no longer correct.
Unfortunately, this error was on three websites, so I did not want to redirect all URL's by hand.

I wish you all the best and a good time!

Many greetings from Berlin

Micha