Scorpion Alarm fob not working?

Please Help! My fob is not working properly for my Vauxhall Tigra - I try to lock the car and the fob works, locks the car and sets the alarm, but 2 seconds later it unlocks itself!!! The alarm is still set though...the only way i have managed to get the car to lock is to push the lock down on the driver door when i get out, then when i shut the door it unlocks itself, but then when i press the fob it locks, and luckily stays locked. I dont know which model alarm i have but it would be an older version as i have a 97/98 model Tigra - any advice would be greatly appreciated - thanks