Anyone can help me with this?
Using the plugin Quick Cache at the same time, but was never an issue before.
I deactivated it, but the error still occurred.
Clearing the cache was not a problem before...
A total of 1 errors occurred while trying to clear your cache. The last error was: Could not create a lock file /mnt/weba/d0/00/0000000/htdocs/website.de/wp-content/wfcache/clear.lock to clear the cache.