Cannot change a password for MSSQL: The test connection to the database server has failed because of an unacceptable password

Symptoms

Cannot change a password for MSSQL via Plesk > Tools & Settings > Database Servers > .MSSQLSERVER20** > Settings > Authentication due to the following error:

PLESK_ERROR: The test connection to the database server has failed because of an unacceptable password

Cause

Strict password requirements/policies.

Resolution

1. Connect to the server via RDP

2. Open Command Prompt as Administrator and execute the following command to open SQL Server Management Studio:

   C:> ssms.exe

3. Go to SQL Server Management Studio > Security > Logins > Administrator > Properties

4. Disable Enforce password policy and Enforce password expiration

5. Change a password for MSSQL via Plesk > Tools & Settings > Database Servers > .MSSQLSERVER20** > Settings > Authentication again

6. If the issue still persists, set  Minimum password length on a Windows level to 10:

   This requirement should be met by the password for MSSQL server.