Do you have the tiger statuette?
I don't know if this is related to the problem you are having now, but I did find this:
Return to the fountain area near the gazebo.
• Zoom into the top of the fountain; place the BRUSH STICK on the moss.
• Put the TIGER KEY in the slot; take the TIGER STATUETTE.
I was thinking maybe the tiger key wouldn't work until you had done this?