If I had to guess I would say that there is too much space above your instep, possibly cuased b the footbeds you got not supporting you correctly.
What type of Footbed did you buy and what type of foam was used to stabilise them? Unfortunatly the North american way of molding footbeds is nowhere near as good as teh European way. Maybe see if you can find a Euro fitter who specilises in Sidas products.
Of course it could be just that your in a bad boot for your foot, but I would guess its more an instep issue.