SAP Business One enter valid username and password

Hi,
I've just installed locally SAP Business One and during my first login with default credentials i get the error "Enter valid username and password".
During the installation i turned my firewall off, also i had SQL Server Browser running and Named Pipes and TCP/IP enabled.
SQL is configured for both windows and server authentication and Collation is SQL_Latin1_General_CP850_CI_AS.
Can anyone tell me how can i solve the problem?