On Linux Plesk server if while adding mysql user or the database  you are getting error as follows

Connection to the database server has failed: Table ‘mysql.servers’ doesn’t exist.

The issue indicates that the mysql version on the server needs up-gradation. The error can be found in /var/lib/mysqld.log 

If it shows error as

114517 17:19:42 [ERROR] Can’t open and lock privilege tables: Table ‘mysql.servers’ doesn’t exist
114517 17:19:42 [ERROR] Column count of mysql.proc is wrong. Expected 20, found 16. Created with MySQL 50045, now running 50156. Please use mysql_upgrade to fix this error.   


You may upgrade the mysql version on plesk server using the below command

mysql_upgrade -uadmin -p`cat /etc/psa/.psa.shadow`

Now restart the mysql service daemon on the server and you shall not get any errors