We are seeing the same issue between 2960X switches and 6506-E's using WS-X6724-SFP and WS-X6516-GBIC cards. (But not between the 2960X and 2960G's.)For the SFP's we've tried various combinations of GLC-SX-MM=, GLC-LH-SM=, GLC-SX-MMD, and GLC-LH-SMD...