I don't know what I'm doing wrong.
I setup a scene with a couple of primitives.
Do a simple animation.
Create a light, a camera and a render node.
Invoke Mantra.
And then I get a black screen and the objects get this zebra pattern…
:cry:

How do you get at Mantra? I have this problem when I render via the camera icon in the viewport. One wrong click can mess everything up, I have even lost work that way. It's a bug of some sort.

But maybe it's something else in your case.

I access Mantra from the Menu Bar:
>>Render>Create Render Node
After I do this I can't do a quick render via the icon on the viewport, just as you mentioned.
The only option that seems to work is, once you have everything ready, just render to a file.
But it sure sucks having no quick render…

Use the MMB on the error'd objects and tell us what the error message says.
And/or attach your file so we can look at it.