Just a bit more info for you on this difference in the behaviour of the Java vs. NET versions of ArcGIS Server with respect to layer visibility. What we observed in the REST Services Directory where specifying for example Layers as "1" in .NET working, yet working Java is still true. However,if you specify the Layers parameter as "show:1", it works in both cases. That latter form is what actually gets passed to the server if for example you turn layers on and off in the javascript API.So it's a very specific case where it doesn't work - that being if you just specify the layers as a comma separated list withoutpreceding it with "show:". In the ArcGIS Server Java that works fine, but in .NET it doesn't.