Alarm system, immobilizer and siren are out of sync

[Glenbinegar]

I am having a problem with my 1999 Sport 350. The key fob works, unlocking the doors and releasing the engine immobilizer functions, but the siren comes on with a load chirp every 5 seconds or so. The fob will cancel the siren operation if the engine is not running but has no effect if the engine is on. When the siren is not operating, the engine is immobilized and can not be started. How do you re-sync the siren and engine immobilizer operation? (new battery in the fob today, no change in operation) Any ideas out there? G;-)