Pancho A8

Hi guys. I have a Audi A8 D2 1997 4.2 and the problem is when I put the D (directly speed) the car start to move and the makes a butting and turns on the lights PRND321. I change the oil transmition and filter transmition but the problem continues. I would like if you can tell me some other tips and a shop where I can buy the rebuild kit transmition.

Thanks in advance and sorry my english.