Hi both,
the previous
thread quoted was responding to the needing of transfeering some map from one server to another (eg. from localhost to the web, or from one domain to another domain).
In case of problems, this strategy may require a little of knowledge about how OGC standards and http works to solve problems.
As users I can suggest the simplest way. Try to add layers to the map is through the catalog, using the UI.
This makes you sure that the server is correctly responding at the address you provided.
Then if you need, you can export the working map and use the URL you find as example for the other maps you want to modify.
Hope it helps.