Thicken: Failed to offset or face could not be deleted.

So I have this surface, and I need to thicken it 0.08" inward. It won't let me.

I KNOW it's failing "Check", but I have no idea how to fix what's wrong with it.

The error message I keep getting is: "Failed to offset or face could not be deleted."

Please help!!

SolidworksSurfacing