Odd rendering problem.

I’ve been trying to get to the bottom of an odd ‘black screen’ rendering problem for the last couple of days.

I spent a whole day thinking I had a camera problem but it turns out to be even stranger. I have around 100 frames of an animation that will not render.

On layer 1 I have a bunch of objects.
On layer 2 I have some scenery, a camera and a path for the camera.
On layer 3 I have all the lights and particles.

During these problem 100 frames - If I deselect layer 3 the renders are ok.
Then if I move the particles to layer 1 the problem comes back.
The particles are active well before the problem frames and they end well after.
The particles are duplicates of a simple icosphere, the most minimal.
I’m well within the memory of my card, Mem906.55m, Peak render 61M and the card is 3Gb.
Nothing else happens of any significance within the problem time period, the camera continues to move and a couple of objects continue to revolve.

I have freed all bakes and rebaked and the problem persists.
I have reloaded the file.
I have reset my PC.

And then, all of a sudden, without making any changes, it starts working again. (Argh!) But this is exactly the same as yesterday and I know it will stop working again.

I have noticed, and this wasn’t the case a couple of days ago, the surface that is emitting the particles is constantly covered with said particles. As if they are sticking to the surface, and sending out a copy, but none of the particle settings reflect this.

I had an odd problem about a week ago when I tried to add some smoke to the scene, I gave up with that as it wouldn’t animate at all, but I can make smoke work in a new project without any issues.

The sudden loss of render is just like I’m overloading the card’s memory, but surely this isn’t the case?

Has anyone seen this kind of behaviour or have any idea what the cause might be?

And I think I might have found the problem.

The particle system that appeared stuck may have been the issue, it was baked but had a cache size of 0. I tried baking it again, it ran through the motions but still reported 0 cache size. I clicked it off the view and render with the little icons, then back on again, baked and presto, it ran and displayed the correct size. And now, everything appears to be ok.

But, I will keep an eye on this. It continues to bother me because I haven’t touched anything to do with the particles for well over a week, so I have no idea why these would have become corrupt or out of date.

While discussing them, is there any preference between internal or external cache data for these little buggers?!