I know, I'm using old software, but I'm waiting on funds for an upgrade, so I'm using what I have.
And what I have are some issues with Maya 2008 and xstream.
Whenever I try to render with Maya hardware, I get the 'unrecognized node' error and the xstreamenvmrshader error in the same message.
As a result, I end up with a black screen render in Mental Ray.
But my scene renders fine with Maya software.
At this point, I'm considering learning how to render the kinf of skies I want to make in Maya itself.