I can not backup one of website's (web20) database. maually backup database is not working but manually backup website is working. on the other side the other website's backups either db or website are working normally.
Check if the mysql root password in the file /usr/local/ispconfig/server/lib/mysql_clientdb.conf is correct.
I've changed the domain for one of the website. I forgot to change site from the database. now it's ok.