Hi!
I've been suffering for a problem with a lof of people here: MR sometimes stops during rendering, and sometime gives a "cannot start thread" message...
Until NOW! Because I found out what the problem was !!!
I'm writing this story to make some people's life easier with telling what the real problem is (or at least was at my case).
When I first tried to render with MR, it went ok. But after some day suddenly it started to freeze at every render (ok, sometimes it rendered 1-2 frames, and stopped only after that). After a windows reinstall, it worked ok, but for some case only, because it kept freezing. The syndrom was: MR starts the frame, and at about half it shows the part of the picture that was "succesfully" rendered, but the other half stayed "blue", no cpu usage, but the window refreshed, so the entire Maya didn't freeze, just MR hangs up, and nothing to do, but to close the process... Sometimes I saw "cannot start thread" error message, but not every time (mostly under win2k).
I was looking for same trouble here on the forums, but I saw only puzzled peoples like me, and had no idea what the problem is.
And in the last 1-2 monthes, I was having really hard problems with my computer. It kept reseting (full randomly). Sometimes it worked for 1 week normally, and then started to reset in every 5 minutes for a few days... It was incomprehensible. I started to replace (I mean borrowing) some components to find out what is wrong in my PC. I tried everything, and the processor stayed last. It was a P4 2.4GHz with 533FSB. I interchanged it with a friend of mine, and after a few hours his computer also started to keep reseting randomly!!! So it became obvious: my processor is bad 
(( I couldn't believe, because it's an Intel processor.. But it's true. (the most bad thing it's out of warranty at my local provider
But ok, I had to buy a new one. I bought a 2.8C (800FSB), installed it, and seen how MR is behaving! AND NOW IT WORKS !!! NO FREEZING after even 50 frame render... So all the freezing was because of my bad CPU !!! Sounds impossible, but it's true And as I looked back in time: I was having this probelm for about a year! And it started to behave _obviously_ wrong only now... I was having a bad CPU for a year, and I wouldn't think some of this "little" error is because of cpu problem... Actually I couldn't seen any other strange thing, that's the weird. Only the MR was behaving strange (and a C++ compiler in the last few days, but not always... but MR always).
And one more weird thing: I have a friend who has the same 2.4B processor like me, and MR does the same thing at him just like me!! I don't know if it's a bad series, but I guess... It's too much coincidence. And I saw someone else here in this forum who has tha same problem with the same type of processor!
I don't want to cause a panic about this 2.4B series, I'm just writing the facts that I experienced...
I hope some of you, who is suffering from this problem founds his solution about my case...
And if so, please let me know.
Best regards,
Dexx