Having read both of the suggestions and progress of the locking /microswitch problems, I too have a similar puzzling Passenger lock mystery.
My Fabia Classic is an all manual locking vehicle. The passenger door locking mechanism fails to unlock the door though the ' pull ' handle on the inside properly triggers the 'Open' button, but does not open the door from the inside or the outside. Furthermore when I put my manual key in the outer barrel it will only relock the button, there is no key pressure felt in the opening direction with the key. Using the methods of Hat Boy Harvey's suggestions have no effect.
I obviously cannot remove the lock barrel until some miracle happens.
Wd40 and PlusGas in the keyhole and door handle don't seem to work either. looking at the pictures of the locking mechanism to release the button and lock are not very obvious. Someone else said they had drilled out their lock so that they could lock and open from the inside. The key is not damaged and I thought possibly the key barrel itself may have stuck pawls as when frozen, or rusted but the lubrication should have dealt with that It appears to be like a screwdriver slot on the inner end. the local garage managed to get it open for its MOT this year- and it promptly locked itself the first time ' opened' from the inside.
I take it that the immobiliser red light when the drivers door is locked does not immobilise the doors - just the engine? operation?
Ian