That screenshot brought back some memories, had not seen that for years. I believe the Tank Umatic was originally controlled by the Grapevine machine (BBC). This was not replaced until after the schedula had become established. Therefore did not feature in the original spec. I seem to remember it mainly played adverts and that our advertising contract may have run out and therefore there would have been little impetus to get the thing going. As to why it did not work I cannot remember.