By blank database.config you mean the one that came with the upgrade?
<connectionStrings>
<add name="AbleCommerce" connectionString="CONNECTIONSTRING" providerName="System.Data.SqlClient" />
</connectionStrings>
I have done that and that is still the error I get trying to access the admin page or the homepage. When I try to run the upgrade it fails quickly saying:
The specified database is not a valid database version. The upgrade only works on AC7.0.6 or higher databases