Why is my SMEG Dishwasher showing E1 without water in tray?

Hi, i have got an older SMEG Dishwasher showing E1.

1. First there was water in the bottom tray. After removing the water the dishwasher worked again.

2. Two weeks later the bottom tray was full of water again, so i looked for the leak and found the leaking o-rings after removing right side panel. Repaired it and made a testrun: All worked fine.

3. After reinstalling the dishwasher to the kitchen i loaded it and switched it on: NOT WORKING AGAIN, showing E1.

4. Opend the machine again - there is no water in the bottom tray and the aqua stop switch is not blocked. I can pull it up with a screwdriver, hear a klicking and then the pump starts working.

5. So the question is: Why is my Smeg Dishwasher showing E1 without water in the bottom tray? Would be so greatfull for any helping advice.