Handbrake new, but makes problems

Hello, I made the brakes completely new with my Omega, everything went so far smoothly. The car is still logged off, but I had already tested the handbrake several times and it felt good. Now I stood with us today at noon in the yard and on a slope and when I wanted to drive away again left the handbrake looked more up…I then played a bit with the coupling that it loosens again, but was really fixed…. nmal there was a blow and she was free. But now it’s so that she pulls herself even slightly again. What can that be, I built everything together again !!!???? Someone a spontaneous idea ?