SharePoint Learning Kit and MLG will only work with the public mapping address set in Central Admin. If you are using a different address other than the default that was set up as part of your install you need to edit it. Link below on how to do it.
If you are configuring your MLG for ISA here is how to do it with your ISA and Central Admin
If you try and use a different access mapping address SLK will try and connect to the default address