I'm having trouble on this solution as well.  I'm pretty sure I've completed all of the steps but am getting the
"Could not find a properly routed case. Ensure that you've setup Omni-Channel correctly by following the requirements."
error as well.  The issue I seem to be having is that after changing ownership of the case to the queue "High Priority", I am not getting a notification in the Omni-Channel widget box to accept.  It just says "You have no active requests".  Does anyone have any suggestions? 

I'm having trouble on this solution as well.  I'm pretty sure I've completed all of the steps but am getting the
"Could not find a properly routed case. Ensure that you've setup Omni-Channel correctly by following the requirements."
error as well.  The issue I seem to be having is that after changing ownership of the case to the queue "High Priority", I am not getting a notification in the Omni-Channel widget box to accept.  It just says "You have no active requests".  Does anyone have any suggestions?