Unable to setup database admin's credentials

[kenken]

After I uploaded a new Plesk license with PostgreSQL, I have been trying to setup a database administrator's Credentials.
However, Plesk doesn't let me create a login and password.
I received the following messages:
"Unable to update database parameters: Unable to change database login: Unable to change administrator's login: Error while execute pg-manager: Unable to start PostgreSQL.1"

I use Plesk vesion 7.5.2 for FreeBSD4.9 that come with Postgresql-server-7.4.6.

Can anybody guide me how to fix the problem? Thank you very much.