MS SQL Configuration for working OK with .NET

Please tell me what special MSSQL config. must do to convince .NET to open a Data Connection. I had error msg
"Exception of System.InvalidCastException was thrown"
when I try to make an connection.
SQL Server Enterprise Manager, Server, Properties, Connections and what Attribute should I choose ?

Thanks,
Best Regards

This is my connection string (sorta):

Data Source=SERVER ADDRESS;UID=USER NAME;PWD=PASSWORD;Initial Catalog=DATABASE NAME

I'm using the System.Data.SqlClient namespace and you can have a connection like this

Dim conSopon As New SqlConnection(Connection String)
conSopon.Open()