There is something very strange about the contest system RandStream... it keeps reverting to a 'legacy' mode randomly. I submitted the same solution several times in a row and kept getting an error since the legacy mode has the State in a cell format. Finally I lucked out and got it to default back to the standard format.

I observed the same effect, it is rather interesting, my guess was that other people submissions including rand('state',...) commands might be producing this (I imagine we should be sharing a matlab session for this to happen, the context might be running on some sort of distributed environment, I am not sure about the details...)