Hi,
Make sure that the user account you are using to do the configuration process is a domain account with sysadmin privilege on both the (Biztalk) application server and the database server.
Before you do the configuration process, make sure that the following four groups are created on the database server: BizTalk Server Administrators, BizTalk Server Operators, BizTalk Application Users and BizTalk Isolated Host Users. Also, make sure that the domain account you are using is a member of the previously mentioned four groups.
I suggest that you uninstall BizTalk before attempting to do the reinstallation and configuration again.
Daniel.