this is the hard edge fault, the solution is to make the displacement map black where there is a hard edge
or to grow up the discontinuity of your object
someone on the softimage list gave this solution:
you can trick the effect of "hard" polygons in the
rendertree, by plugging the "Vector_state" node set to "Geometric
normal" mode, straight into the Bump input of the material node.
hope this help