If a mysql table was corrupted for some reason, one can try repairing it using the following command line:
%plesk_dir%\mysql\bin\myisamchk -r TableName.MYI
C:\Program Files\SWsoft\Plesk\MySql\bin\myisamchk -r TableName.MYI
Note: The latest Plesk versions use Mysql which is configured to use InnoDb format. This solution doesn't work for them.