How to fix Kenwood Slimline Dishwasher KDW45X20 with a F1 Er?

my Kenwood Slimline Dishwasher KDW45X20 keeps giving a Fault Beep F1, after about 15/20 mins or so into the washing cycle. i've tried emptying the tray underneath once (perhaps not fully done), but the fault appeared again. I don't believe a side panel can be removed, only the silver tray around the dirt sieve/gatherer. Please tell me, What should I do?