In order to troubleshoot the connectivity of the request between the client and the server, we can enable the remote debugging that will allow the Administrator to call the webservice methods as it was locally in the server.
In order to enable this, you will need to add the following lines, after the <system.web>, to the web.config of the webservice you want to debug:
<webServices>
<protocols>
<add name="HttpGet"/>
<add name="HttpPost"/>
</protocols>
</webServices>
Saving the web.config will allow you to, for example, invoke the getConfigVersioned when calling the mlsservice.asmx remotely, from a user machine.
After the debug, we highly recommend you to delete these lines or comment them with <!-- at the begging of the XML block and --> at the end.