Well, for starters.. this wouldn't prolly solve anything.. but try resetting the x-form.. it's something I always do when I get wierd errors, usually works.. though it should only affect transformations/deformers and normals as far as I'm concerned.. might want to try it anyways though.
And if you're sure the lowpoly cage and highpoly model isn't intersecting.. then.. well, what could it possibly be.. I know I had this error aswell once, never managed to solve it really.. So i'm not quite sure.
Well, I'm sorry mate, but I can't really pin down the error
Cheers