Hi @Domi7, I am sorry to hear about this.
Your question has been translated to English as this is an International support forum. Please post any replies in English and it will be easier for me and other users to assist you.
The first thing I would suggest in this situation is to reboot your phone in safe mode in order to see if you receive the same error message appears there. All apps downloaded from Play Store is temporarily disabled while in safe mode and by doing this, you can see whether this behaviour is caused by a downloaded app in your phone. For more information on safe mode and how to use it, click here.
If the same error message appears while in safe mode, I suggest that you try to perform a software repair using a computer and Xperia Companion. Please note though that a software repair will erase all user data, so remember to do a backup of your user data first.
Try this and let me know how it goes!
