Error with ConnectionString

When I attempt to configure a connection to the database using a user ID and password I get an error "Login failed for user X" when NHibernate attempts to use the connection:

Here's how I am attempting to confgure the database connection:

MsSqlConfiguration.MsSql2005

             .ConnectionString(c => c.FromAppSetting("DbConnection"));

My App.config has this:

<add key="DbConnection" value="Data Source=MyDBServer;Initial Catalog=MyDb;User ID=x;Password=y"/>

However if I change my App.Config bBConnection property to use integrated security everything works fine!.
i.e. my app.config now looks like this:

<add key="DbConnection" value="Data Source=MyDBServer2;Initial Catalog=MyDb;Integrated Security=true;"/>

Also if instead of using the 'FromAppSetting' method to configure the connection string if I use the MsSqlConnectionStringBuilder Username/Password methods then I don't get any errors either.

i.e.
MsSqlConfiguration.MsSql2005

             .ConnectionString(c => c
                                         .Server("MyDBServer")
                                         .Database("MyDB")
                                         .Username("X")
                                         .Password("Y")

Any ideas? I'm trying to use the FromAppSetting method because I want to specify properties such as 'Connect Timeout' and 'Max Pool Size' which do not exist as methods on MsSqlConnectionStringBuilder.

I'm using fluent nhibernate 1.0.0.593.

Thanks