Subcanonical Graded Rings Which Are Not Cohen-Macaulay, with Appendix: A   non-Q-Gorenstein Cohen-Macaulay cone X with K_X Q-Cartier
  The paper answers a question by Jonathan Wahl,giving examples of regular surfaces S (so their canonical ring is a Gorenstein graded ring) having the following properties:   1) their canonical divisor K_S = rL is a positive multiple of an ample divisor L   2) the graded ring R := R (X,L ) associated to L is not Cohen-Macaulay.   In the appendix Wahl shows how these examples lead to the existence of Cohen-Macaulay singularities with K_X Q -Cartier which are not Q -Gorenstein, since their index one cover is not Cohen- Macaulay. 
Fabrizio Catanese (Universitaet Bayreuth), Appendix by Jonathan Wahl   (University of North Carolina, Chapel Hill)
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