It sounds like perhaps the script was killing by procwatch. I've had that happen only once before, but it didn't display any error as in your situation - it just died, heh.
You might wish to try the development script posted here.
Otherwise... I'm not sure what to suggest. If your server's load is really high I can see procwatch killing the install, or if your user-space is using up nearly all of its memory already, I can see it happening because of that as well.
Chips N Cheese - Custom PHP installs and the like!