I have noticed a few things from dealings with this flaky software. I started with 4.6 and didn't have too many problems overall except for the occasional error 51 issue. Using a script someone (sorry I can't remember who wrote it) wrote, it would reset that issue.
Then I upgraded to 4.7 and didn't have any issues. But then my iBook G4 died suddenly so I got another iBook G4. I reinstalled 4.7 and noticed now too that I had a visible alias on the disk for the opt folder. If you delete or move this alias, VPN will crap out and simply not work. The restart script will not work with this issue at all. As long as that alias is there, it works. Anybody know what the story is with this? I could have sworn that on my old iBook G4, I did not have this alias visible. In the console, the error message is stating something about not finding something to start up if the alias is missing.
Also, one thing I found interesting but don't know if it really did anything or not. A comment from VersionTracker or MacUpdate (can't remember which) said that if you had ever had sharing through firewire on, it should be off. Just to try anything to get this flaky program to work, I turned it on and then turned it off. Just a thought but certainly no promises.