Dash Button with Hue Lights-rule doesn't work

my setup is a raspberry 1st. gen with the newest stable Version of openhabian / openhab2. All things (hue bulbs and the DashButton) are recognized by the System - along with my rookie-skills i’ve made all preferences by the paper ui … including the rules setup. This was done by the “rule engine (experimental)”.
My rule starts with the Channel “Dash Button (press)” and the Event “on”. The"send a command"-section incluedes the Item “colour hue button …” and the command “on”.
If I do a little test by the “play”-Button in the rule the lights go on - so i think there is no error in the “send a command”-section. I think the problem is in the “when…”-Section with the DashButton.

My first idea was to check log-files … but the logs i’ve checked where empty (events.log) or only had old entries (openhab.log). Are there other logs? … or do i have to start the logging of acitivities and rules in a separate preference?

Thanks for help