ERROR: PleskMainDBException
DB query failed: Unknown error

0: common_func.php3:171
db_query(string 'set names utf8')
1: common_func.php3:626
reconnect()
2: common_func.php3:591
db_connect()
3: auth.php3:90


Cause

The Parallels Plesk Panel administrator’s password and Plesk SQL Server administrator password are corrupted.

Resolution

The passwords for the Parallels Plesk Panel administrator and the Plesk SQL Server administrator must be reset:

1. Find the username of the Plesk SQL Server administrator in the PLESK_DATABASE_LOGIN value in the registry key HKLM\SOFTWARE\Plesk\PSA Config\Config.
2. Open the file %plesk_dir%\mysql\data\my.ini and add skip-grant-tables to the [PleskSQLServer] section. Save the file and restart Plesk SQL Server service.
3. Log in to SQL:
   "%plesk_dir%\mysql\bin\mysql" -P8306 -Dmysql
4. Update the password of the Plesk SQL administrator (replace NEW_PASSWORD and admin with proper values):
   UPDATE user SET Password = password('NEW_PASSWORD') WHERE User = 'admin';
5. Remove skip-grant-tables from %plesk_dir%\mysql\data\my.ini. Save the file and restart Plesk SQL Server service.
6. Set a new password for the Parallels Plesk Panel administrator:
   "%plesk_bin%\plesksrvclient" -set NEW_PASSWORD

Kaynak : http://kb.parallels.com/en/115602