I had the same problem mentioned here, so I logged in as webuser on mydomain.de/phpmyadmin and executed the query from the most pupolar answer:
GRANT ALL PRIVILEGES ON *.* TO 'webuser'@'localhost' IDENTIFIED BY 'webuser' WITH GRANT OPTION;
After that, I'm not able to login to phpmyadmin anymore with user=webuser.
#1045 Cannot log in to the MySQL server.
But on my website (subdomain.mydomain.de), where I use the same login to connect to my mysql-database, everything is ok.
What have I done and how can I fix this?