ispc cron log error

[pawan]

in the monitor module under ispc cron log:

These errors are repeating continuously. what could have gone wrong?

PHP Warning: mysqli::query(): Couldn't fetch db in /usr/local/ispconfig/server/lib/classes/db_mysql.inc.php on line 107
PHP Warning: mysqli::escape_string(): Couldn't fetch db in /usr/local/ispconfig/server/lib/classes/db_mysql.inc.php on line 166
PHP Warning: mysqli::ping(): Couldn't fetch db in /usr/local/ispconfig/server/lib/classes/db_mysql.inc.php on line 106

[till]

Is the mysql server down or the dbispconfig database inaccessible?

[pawan]

No mysql server is working fine. i can access all database through phpmyadmin.

what else should I check?

As a Hint, I have linked all websites to database and username for enabling database backup.

for most of the websites, I am getting the DB backup excepting some.
could it be related to this?