I encountered a very strange RE today on 1270F - Awesome Substrings.
The only difference in my accepted solution was updating MX to a slightly smaller value (350 -> 300) (and correspondingly updating MX2 to a slightly larger one) so that the very big array became smaller.
My theory is that the big array in the failing solution uses up more than 256MB, and exceeds the stack size of the machine... Except that the memory limit in the problem is 512MB and so that shouldn't be a problem :/
The idea that you can't submit something and be pretty certain that it passes just drives me nuts. Any thoughts?