Forgot to add details: win7pro 64 bit, Arduino 1.5.2, USBASP (Ebay clone) with latest firmware from fischl.de. Programming an arbitrary sketch into the MEGA328 on the Duemilanove works fine, and I can burn a bootloader into the MEGA2560 board successfully. But uploading a sketch into the MEGA2560 does not work, the board stays dead with the blink example and other sketches naturally don't load as well.