What a disapointment!!!
All of my WMS Services which can be loaded easily and correctly into all versions of desktop ArcGIS and other opensource brands of desktop GIS as well as my Webapps, cannot be shown in ArcGIS Explorer!
The layers from the service are listed when the connection is made, and the layer is loaded into ArcGIS Explorer..but that is where the fun stops. No Features, no error messages, nothing.
What is the use of ArcGIS Explorer when you can´t load external wms services into it?