Polo 6n2 diagnostics communication error?

Hi

I currently own a 2000 1.4 6n2 16v polo and just recently changed my pedal box however in the process I didn’t connect my air bag sensor connection and now after connecting it the cars registering it as a fault.

Now heres the problem, I ve had 3 different mechanics look at it with different dialogistic systems with all three having the same problem of not communicating with the car.

Any ideas were the problem could be as all three say there are usually no problems with vw and audis yet my car doesn’t want to communicate with any devices.

Any ideas people…

Really scratching my head now?! Lol

Cheers in advance

Mitz!