stuck in the bonus game

HI! can anyone help?
I'm willing to burn the rope at top of the falaise but i can't do it.
I played the game in french and the SG tells me to burn the rope with the magnifying glass but it doesn't work, the magnifying glass jumps up and returns to my inventory.
Do i need a mirror instead?
May be the french version isn't the same as the english one...
Help please, i'd like to finish this one...

put the mirror down by the sign and click on the rope. put the magnify lens where the blinking light is and that should burn the rope. you get the strategy guild if you have the collectors edition. if its like the english version, its in the upper left corner marked guide. good luck.