sorry, the alarm will need to be reset back to factory codes, you may require the service of a local alarms company. book it in for a service and ask about it then,check their prices over the phone. quite a common panel so should not be to much of a problem.
beware of its age though, about ten years is a good age, so my advice, if its round about, it may well be more cost effective to think about renewing/ updating it.