I have a proxy object generated by Visual Studio (client side) named ServerClient. I am attempting to set ClientCredentials.UserName.UserName/Password before opening up a new connection using this code:

InstanceContext context = new InstanceContext(this);

m_client = new ServerClient(context);
m_client.ClientCredentials.UserName.UserName = "Sample";

As soon as the code hits the UserName line it fails with an "Object is read-only" error. I know this can happen if the connection is already open or faulted, but at this point I haven't called context.Open() yet.

I have configured the Bindings (which uses netTcpBinding) to use Message as it's security mode, and MessageClientCredentialType is set to UserName.

Any ideas?