ford transit immo light flashing very fast ?

i have a ford transit 1997 model the immobilizer started flashing very fast and the car will not start but if i remove the battery head and fix it back i will turn the key on and it come solid i mean the immo light and the car will start now the car can not start again even when battery are remove. they have try reading the eepprom and reprogramming another key still the same fault the light still flashes very fast, will it be that immo box need to be changed or what can be done to start this car even it amount to bypassing the security is even more better for me thanks