thats mad i only did the same job yesterday and all because of my rear number plate light not working , all i can say is have a close look at you bumper support i brought a replacement one before i started because mine was very rusty and im glad i did because when i got it off it fell in half ! pretty easy to come off though , just 6 bolts underneath and a 2 clips either side of the car and make sure you disconnect your numberplate lights , you probably know this anyway ! not sure what else to look for though , i suppose just make sure theres no damage to the rear end behind the bumper .
cheers mark