Check drain light fault on a Miele Novotronic W827 ?

I have randomly occuring drain light fault that appears on my miele novotronic W827. It seems to occure at any stage of the program where a drain is required and not always at the same stage of the program ie sometimes at the first drain in the program and sometimes right at the end. Some of the time it will work perfectly ok for 2 or 3 washes and then plays up again 3 or 4 times. I have checked the pump which works fine I have checked the drain, checked all the pipes which are all clear all to no avail. Help!