Did you figure this out? I have this problem in Win7 x64 as well. 6 R9 290x, only able to get 3 running. Anything more than 3, randomly selected it seems, will throw Error -4.

I resorted to using BAMT and that worked well. But I really want to use some modified BIOS that only work with 13.12 WHQL drivers, something that the linux distro can't provide.