Tila Tequila

"open door" warning light on VW Polo stays on!?

I’ve got a VW Polo 1.6 2006 hatch and I just had new brake disks and pads put in now and when I had left the garage I noticed the “open door” light (passenger door) was on – as if the door wasn’t closed properly. I checked the door and it was closed properly!

All doors are closed properly but the warning light still stays!
Also, now I can’t lock the car via the key because the car thinks a door hasn’t been closed properly.

What do you think my problem is?
Car door sensor? That’s the only thing I can think of!
Is it because I had got new brake pads and disks put in or is that just a co-incidence?

Appreciate your help!