Lockup isue with 5 wow's

First post here, I appricate any help.

I started multiboxing for the first time last night, I've got everything working rather flawlessly with 4 accounts... but when I add in the 5th, the entire system freezes. The screen freezes like a full-size screenshot, and the sound studders until I hard-reboot the machine.

5 spereate copies of wow on the hard drive.

Using keyclone & maximiser for 4 copies.

I appriciate any help, I've already checked temperatures, run a memory test and updated drivers. I've got a performance monitor on my G15 and it doesn't say anything is maxing out at 100%...

System specs:

Quad Core, 4gb 1000fsb ram, 2x8800gtx SLI, 2x raided raptor 10,000rpm hard drives ((Running Windows Vista x64))

I would highly recommend turning off ALL sound on all accounts/instances of wow. Next make sure that all video settings are pushed to the bare minimum.

Next I would open up each copy manually 1 at a time without the aid of Keyclone, just to test if the machine can run them all.