first of all welcome to openHAB.
Please post in English as this is an English speaking community - even if many of us may be German you will have a better chance to get help posting in English as many very experienced users are from other locations and do not understand German.
As for your problem:
Please give more detailed information about your rule, first see How to ask as good question
What is the release you are using, what is the content of your file, how does the log file look like (-> Frontail) when saving the rule file?
How are you editing it ? I´d strongly suggest to use VSCode as editor, it supports syntax checking and auto completion.
Maybe you simply have a typo or a syntax error in your file.
Without more information it is hard to help you.