gilldavies

Hi all, I'm a new member and hope I've put this in the right place.. I bought a second hand 118d sport about 8 weeks ago now with a 3 month warranty. A few days after purchasing it, whenever I pulled away in 1st gear, the interior light came on and a warning that the driver's door was open showed on the dash. The driver's door was not open. Apart from being very annoying, I can live with it, but I can't live with the fact it will not lock because it thinks the door is open. Sometimes it does lock but the alarm goes off, then it won't lock either with the remote or manually without the alarm activating, so more often than not I have to leave it unlocked. I have had the driver's door lock changed under the warranty but that has not solved the problem. It has also had a diagnostic check at Vines of Guildford and apparently found no faults. I took it back again and they found 7 faults with the alarm but no explanation. They have said if I want to throw loads of money at it, they can investigate by dismantling the driver's door, but I don't think the driver's door is the problem. If I don't open the offside passenger door, it drives without any driver's door warning on the dash, but if I put anything in the back, the problem starts from the moment I leave my garage in the morning. Yesterday I arrived at my destination and locked the car, but then returned to put some shopping in the boot, locked it again and the alarm went off. It wouldn't then lock with either the remote or manually. I really regret selling my Mercedes to buy this car and regret buying a BMW because there seems no rhyme nor reason for this fault and no explanation from the dealer of the cause or how it can be fixed. If anyone can help I would be eternally grateful!