Why is my dryer saying this?

you do not give the make of your dryer,i bet its a hotpoint or an indesit (same machine )your prob is at the rear of he machine
looking at it from the rear its down the bottom of the machine a gray unit its the float chamber and the float has stuck down,remove the plug from mains socket and r emove the cover of the float chamber clean it out then put it back together you will then find it works fine common fault its the gray unit at the bottom left of the machine

gts
March 2016