Singularities of the 2-dimensional moduli spaces of stable sheaves on K3   surfaces
  We consider the singuralities of 2-dimensional moduli spaces of semi-stable sheaves on K3 surfaces. We show that the moduli space is normal, in particular the singuralities are rational double points. We also describe the exceptional locus on the resolution in terms of exceptional sheaves. 
Nobuaki Onishi and Kota Yoshioka