Scantronic 9448 Tamper Light?

I have recently moved into a house with a scantronic 9448 alarm system.

Unfortunatly my dog ate through one of the door sensors, so I have replaced this, and also replaces the battery which was dead.

However, when I try to set the alarm it will not set and the zone 1 (where the door sensor was) and tamper light flash alternately.

Could anyone please advise how to reset this.