Ok, just like many others here i also ran into the problem with the heated bed.
Here is THE way to fix this problem, it works !
The problem is on the board itself and is caused by the thin ( to thin ) lines that go to the contacts for the temp sensor.
I took out my heated bed to inspect the soldering, looked fine but still the bed caused problems, the temp goes crazy, runs up to 150 degrees + and than you get the error.
this is how to solve it permanently..
remove the screws on the block where the 4 wires are attached. You need a soldering iron on 385 degrees max.
remove the block and clean the contacts on the board and the contacts on the block.
Than put new soldering on the contacts on the left ( the ones that heat up the bed )
solder the block back but only the 2 contacts on the left.
Now take 2 thin electrical wired and solder them on them on the block on the right ( for the temp sensor )
In the picture you see the brown wire goes to the sensor on top, the red one goes to the sensor below.
solder the 2 wires there and it works like a charm again.
Here below is a picture of the solution, i think that everybody who has worked on the heated bed can recognize this and sees how the solution works.
I found out that the lines on the board for the temp sensor are very very tiny, you can not resolder them, to little.
but with these 2 bypasses, it works perfectly again
Good luck
Marco