  The main outcome of this paper is that the variety VSP(F,10) of presentations
of a general cubic form F in 6 variables as a sum of 10 cubes is a smooth
symplectic 4-fold obtained a deformation of the Hilbert square of a K3 surface
of genus 8. After publishing it in Trans. Am. Math. Soc. 353, No.4, 1455-1468
(2001), it was noted to us by Eyal Markman that in Theorem 3.17 we conclude
without proof that VSP(F,10) should be the 4-fold of lines on another cubic
4-fold. We correct this in the e-print "Addendum to K3 surfaces of genus 8 and
varieties of sums of powers of cubic fourfolds" (math.AG/0611533), where we
establish that the general VSP(F,10) is in fact a new symplectic 4-fold
different from the family of lines on a cubic 4-fold.
