Does it spend a lot of time sitting on a heat mat/hot rock/ warm surface??
It looks like the shedding oils along the ventral surface have dried out prematurely from sitting on a warm surface for too long while in the milky stage of shedding. The oils dry, and this causes the old skin (which is about to be shed) to stick to the new underlying skin. When this happens it looks just like your snakes condition.
If this is the case then get it off any warm surfaces until after it sheds. A day or two before you think it will shed, give it a warm bath to soften the skin - it's gonna need it!! In such cases as this, when the snake sheds it's skin it will pull the new skin off with it in that area. This can cause permanent scarring.
I hope i'm wrong, but....
p.s. There is also the chance of it being scale rot, depending on your set-up.