Hello.

1. Check the database user access rights to the database.They must be full.
2. Look at the logs on the server. There may be more details.
3. Contact the technical support of your hosting.

My new database provider "one.com" uses Mariadb. (I had Mysql before and it worked fine). I can read the database but not create a new record or edit a record. 

Why is this? is Maria DB not compatible with Mysql? 

I just want to add that i use the dataviewer in Website x5! I get "Error Can't perform query"

try the engine InnoDB 

"I had Mysql before and it worked fine" - try switching back to Mysql.

The database is always mysql, what changes is the engine that makes it work