Render Lockdown

JOdel

Got a scene. Reasonably complex. 3DLight, using mostly lights and skydome that I've used before without problems. It spot renders slowly but it does it. 

Set it to render the whole scene and nada. No render. Five and a half hours claiming that it's rendering and nothing has happened. There is no render. It hasn't even started the actual render.

And then the program hangs when I try to cancel the render. The empty render window won't go away and the "render" never quits. Have to force quit the program.

Now, it occurs to me that I *may* have some idea of what is going on. I'd like confirmation.

The one light that I haven't used before is a sun light with a parented spec light which came with one of the sets that the scene is composed of. I suspect that these might be Iray lights. In addition; the sun light came set with a Deep Shadow map. I changed this to raytraced shadows. 

Is this what is likely to be locking the render up?

ETA: Well, it isn't the lights. I replaced all of the lights with lights I'd used without any issues and then set the render up and went off to run errands.

Six hours later, I come home to an empty render window and having to force quit Studio to make it go away. 

Any suggestions of what is doing this?

JOdel

No one?

Some further information then.

I deleted some of the foreground elements and the scene did fianlly start rendering. Very slowly. Admittedly, there were trees. 25 hours later, and at something like 70% done, I canceled the render and saved what I had, Intending to render the bottom portion of the scene with the foreground elements and layer them. I deleted the background elements and saved a copy. 

The partial scene refuses to render. I can no longer assume that this is due to the complexity of the scene, because the scene is now decidedly simple. A ground plane with a water plane, two tree trunks, some additonal plants. 

And not only will it not render, it will not cancel a render. The counter keeps track of the time, but nothing is happening. Telling it to cancel makes the cancel button go away, but the empty render window does not close and the program has to be forced to quit.

This happens with Studio 4.10 AND 4.9. Neither version of the program will render the scene. Replacing the two treetrunks with fresh copies.does not change the behaviour.