Hi @Sandra13, sorry to hear about this.
Your post has been translated to English as this is an International forum, please post any replies in English and it will be easier for me and other users to assist you.
As @Okimntngr mentioned, the first thing that i would suggest if clearing data for the app do not manage to start the camera is to reboot your phone in safe mode to see if the camera app works better there. By doing this you can see whether this error message is caused by a downloaded app or not.
If the same error message appears in safe mode, you might need to repair the software on your phone using a computer and Xperia Companion. Keep in mind though that a software repair will erase all user data, so make sure to do a backup before the repair in order to prevent loss of data.
Try these measures and let me know how it goes!
