hoover d/w hed6612 4 lights flashing?

i got called out to this machine about a month ago with all four of the lights flashing (apparently overfilling) i checked the machine but couldnt find a fault, just been called back for the same fault and not found anything again,any ideas what could be causing it? they have changed the detergent recently, they was using finish but now on fairy ive told them to go back to finish to see if it still does it.

many thanks paul