[dvsone1440]

I was having the same issue before I added the grass in 2.7 so I think it is not directly related to the grass... Although it does seem to happen the more complex the model gets so anything that adds stress to the system I am sure does not help.

I actually forgot that I had been playing with displacement on that model... but did not realize that I should be applying that to the components not the planes.. thanks for the heads up on that.

So... sounds like there was nothing wrong with the HDRI's I sent you?... they are just memory intensive and thats helping cause the error?
...and for the time being try to keep the memory down to hopefully work around this issue?
I can usually make it work eventually.

[JDHill]

Yes, I was not specifically implicating grass, but 2 million blades of it is a pretty good way to get toward memory limits. And also, yes, my testing has ruled out your HDRI as being the culprit. I proved that by making an array of 16 copies of your scene (with grass disabled) and rendering that; with this scene, I am able to a) trigger the behavior by selecting a large HDRI, b) un-trigger it by then selecting a small one, and c) perform steps a & b repeatedly. I could not say whether there is anything that can be done to improve this or not, but I've made a screen video showing the process, and will be giving that to the core engine developers, so they can see what's happening.

Regarding displacement, there is no rule that says you should apply to group/component -- you only need to avoid face-assignment of displacement temporarily, due to the bug with multi-materials vs. displacement in 2.7.

[dvsone1440]

That's definitely the behavior... I can just click back to physical sky or a smaller HDRI and it will run. Restarting sketch up usually works as well.

Thanks for your effort looking into this, hopefully they will find the problem for the next release.