I have just started to have trouble using the thicknesser of my planer thicknesser. When I pass a length of timber through, it always lifts and gouges out the last few inches as it is not fully supported. I have tried using a roller stand to support it but it is still the same.

First of all ensure the piece of timber you are trying to thickness has been correctly planed, leaving you with a perfectly flat datum face on which to run the material on through the thicknesser. Make sure the thicknesser table is regular treated with silicon spray (CWA195) or a good quality wax to give smooth running through the thicknesser. Finally if you are still having problems make sure the knives on the thicknesser block are sharp set at the correct height.