The message is probably shown due to the fact that FS froze, not the other way around.
Did you do something special when this happened? No gdb debugging going on or something like that? I can't find any reason why this would happen, except that the server was over loaded, or something else in the kernel happened. Every channel has it's own thread. So if something would freeze it wouldn's show up like this, maybe in a single call or something. So the only thing I can see right now in an over loaded server - even though it sounds strange, since you have 16 cores...