I assumed that the blue wire was connected to neutral as it was tagged with a black ring. The original set up only worked because the permanant live (your red cable) never came into contact with the blue cable. The switch was either connecting L1 to L2 or L1 toL3 but L2 and L3 never make contact. Your first attempt with the dimmer connected the live to the neutral and destroyed the dimmer. Your second attempt with the dimmer may still have failed even though it followed the original wiring diagram. As some lightswitchesdo not always make a clean break between the contacts as they are switched and you may momentarily get all 3 terminals touching each other inside the switch. The result would have been the same (ie destroyed dimmer)
The wiring as it was originally done was incorrect, so have a look around your house at the other one way switches and see if any others are wired up in the same way. If so then terminate any blue wires with a black tag with some strip connector. The main fail point would be that the yellow wire is marked as live using a red tag but it is obviously neutral when the light is switched off
Adam