Level 11: can't cross the gap to the Shaman

Hi folks

Sorry if this is a repeat on here. I have a green circle to cross the gap, and it asks for 10 food. I have plenty of food, but the game won't let me cross the gap. I've closed down the game and come back, and I've done all the building I can. I think it must be the Shaman who gives you the final crystal skull for the cave game, so I'm feeling a bit frustrated. Please can anyone help?

All the best, Jan