Right click your login that you created in SQL Management and choose properties, then click User Mapping. Select your mojoportal db in the top pane then select db_owner in the bottom pane and click ok to save.
The other thing is to make sure SQL is configured for mixed mode authentication which allows both windows users and sql logins to connect. Right click the very top node in SQL Management and choose properties, click security then make sure SQL Server and Windows Authentication is checked.
It also needs to be accepting network connections. You'll need to open SQL Server Configuration Manager to check this, I think some of this may be disabled by default in SQL Express. Under Native Client Configuration > Client Protocols, make sure tcp/ip is enabled.
Hope it helps,