Skoda Fabia door open FAULT sensor?

I have a 2001 Skoda Fabia Elegance 1.4 16v.
All has been great until today when the display panel bleeped and told me that A door was still open. I opened the doors and firmly closed all of them but still the warning light remanins on. It will now not let me use the key to lock the car remotely.

Any ideas or suggestions please...