I've run some tests using the same version of PicoScope 6 with square waves. I've found that the trigger works using your settings (I changed the trigger type to repeat).
I varied the signal from around 1kHz to 30kHz, and found that above 24kHz, the scope does not trigger as the width of the pulse is 20us.
Just a few things to check:
- Click Help -> About PicoScope 6, what is the driver version?
- Please ensure your probe is set up correctly - have you adjusted the probe at the x10 setting?
- Does the signal appear correctly in terms of amplitude with no trigger?