pylon:
HighFuse to F9 disables ICSP programming. If you don't have a high voltage programmer, get a new chip.
I added a small hack to my AVRDUDE. Before programming a chip, it checks if HFUSE, bit 5 (SPIEN) is going to be un-programmed and if so it prints a warning saying that this will disable further programming and can only be recovered by using a high voltage programmer and do you REALLY REALLY want to do this?
It's saved me a few times from doing something stupid when I've been up all night programming and my brain has since turned to mush... 