Maybe I need to add a pull down to B0 too, though I still cant explain the strange results I was getting.
Anyway thank you for your help, I'll have another go at the weekend.
Hope I can get it to work, I love how fitting an encoder to the board made it an encoder with push button switch underneath, so just pushing the knob gives me an encoder with a switch, totally by accident, not design.

Amazing, & puzzling how I can write a USB interface, write the visual basic program to connect the hardware to flight simulator, and then I cant even get a switch to work.

By the way much kudos, & many thanks for your interrupt routines, they made a project at work really easy for me.

Kind regards
Bob...