Complex sentence: After 28 May 2011 at 00:33,1967 Stock trains were no longer able to run to stations north of Seven Sisters, because of the commissioning of a new, incompatible signalling system (and decommissioning of the old one) between Seven Sisters and Walthamstow Central.
Split into simpler sentences: After 28 May 2011 at 00:33 1967 Stock were no longer able to run to stations north of Seven Sisters. This was due to the commissioning of a new incompatible signalling system (and decommissioning of the old one) between Seven Sisters and Walthamstow Central.