The screws either missed or not gone in enough or too much it's that f**k**g simple, some of the answers on here are embarrassing from so called plasterers. It's basics and very basic, you can make as many excuses as you can and blame as many people as you want but at the end of the day it's the guy who put the screws in simple. This is the problem with everyone jumping on the trowel as soon as they buy one, they haven't got a Scooby doo about the very basics, that's where going to college and learning comes in ( fair enough some of the lecturers know even less). People need to start from the beginning rather than jumping in in the middle and polishing a wall it is embarrassing reading some of the s**t on here from regular posters who have sometimes actually served their time on here.