Not sure if it's the same problem that you're having, but every time I tried installing the voice patch I got spammed with "Cannot open voice file" (or something similar, I didn't write it down) error messages at around 70%.
I finally found out that either my anti-virus (avast) or firewall (zonealarm) caused some pretty nasty memory leaks during install. Never occurred while installing other programs, but then again, no other program processed 30k sound files
Hit control+alt+del when you get the error during the install, if your commit charge is something ridiculous (I had a peak of over 1.
gigs) then most likely you're having the same problem as me.
I disabled my firewall and antivirus software (after disconnecting the computer from the net, can't be paranoid enough). After that, the voice patch installed just fine.
Hope it helps.