Miele Novotronic excess detergent only with towels

Hi,

When we wash anything other than towels, all works well. When we wash the towels, even splitting the load to make it lighter, we usually get the ‘excess detergent’ light – and the machine does not drain. Emptying the drainage system, by removing the screw plug, solves the problem in that a separate rinse and drain then both rinses and dries the towels. As previously stated, all other clothes, sheets etc all wash without any problem. Any ideas please ?