Hoi Dick,
Can you share orginal message in ENGLISH version - then please also search on forum.joomla.org
But in general it doesn't look like from our extensions/template but problem from Joomla itself. I found many topics from the past in offcial joomla forum.
Tip that may help:
- In Joomla Admin access Extensions-> Extensions Manager -> Discover -> Purge Cache.
- Then Extension Manager -> Database -> Fix.
- Go to Extension Manager -> Discover -> Discover.
- Install all found extensions/plugins.
- Publish some of them