I can't thicken a surface

Hello everyone,

I need to thicken Surface-Knit1 0.50 mm outward. But it says "unable to thicken the surface". I tried to change the knit and to find the locus of the problem. It seems it is the part at the front corner of the mouse in that knit. However I can't manage to understand what causes it exactly and solve it.

I would really really appreciate your help, I really want to understand the problem.

Thanks.

SolidworksSurfacing