Pico: strange behaviour with setWatch on BTN1

Thank you for your questions/answers. I did some tests and measurements so, here are my answers :

• What does your volt meter say when the Button is pressed? : it says 0.00 v. I changed the wire which connects to the pico header. Same effect.
  
• When pressed - connects pin B10 to GND - correct? Yes, it is wired to the ground. I also checked with the ohmmeter.
  
• What kind of button do you have? It is a http://www.farnell.com/datasheets/1825221.pdf microswitch. 01L series. I did several objects with these OMRON switches that are quite good and have very low and fast bounce. It is brand new. I will change it and give you the result of the new tests.
  
• I tested with various debouncing duration, but it has no effect.
  I come back to you with test results with another switch.
  Best regards
  GB