Why would a whole region have severe difficulties with the railway "signalling system"?
The problem may be a minor one with just a couple of signals, but the complete shutdown of that part of the network is a safety measure. 

Trains should stop at red lights. New systems will do this automatically, but for instance in Belgium it was only introduced in all trains after a few bad accidents had happened with many casualties. If the automatic stop system isn't implemented yet and just signal doesn't work or work reliably the red light might not show, the train won't stop and may crash into another one.

The reason of the failing signaling could be anything, it's no use speculating without further details.