I´ve found a solution in another forum, her it goes:
You will need to use the SQL Server Management Studio in order to get this to work. When you log into the SQL Manager, You select the P6 database. Right click and select: "New Query".
In the right pane you will need to paste the following script:
Exec sp_change_users_login 'Update_one','PUBUSER','PUBUSER'
Exec sp_change_users_login 'Update_one','PRIVUSER','PRIVUSER'
and select "Execute" from the menu. The connection to the priv- and pubuser is reastablished.
Now you will no longer receive the "Bad Public user name & password" error.