Single and double lights on filter size keep flashing

Make sure you lock the hopper and the bean reservoir completely. lock it and the lights will come back to normal.. This is a safety feature when the the single and double lights flash intermittently, (back and forth).

Thanks, cleaning the hopper is the answer!

Same thing happened to me this very morning and I found the answer above worked-I unscrewed the hopper completely cleaned out some residual beans and then put it back and sure it was locked and the lights stopped flashing and it worked