You have tried to use the remote switch with the key to disable, right?
On my Viper-equipped rig, there is a small steel plunger installed on the left side panel down at the same level as the brake pedal. Depress that while turning the ignition to half cock. There should be some kind of two-stage click as the alarm disarms.
My stupid system will arm itself sometimes; seems like cold weather has something to do with it, but I can hardly imagine why.