It wasn't the simple one-off bomb mentioned on your site - I kept clicking Restart and the error message kept reappearing without an actual reboot taking place. Pulled the power, booted with Shift pressed down, went into Extensions and moved a bunch of stuff (including Apple Built-in Ethernet) to Disabled Extensions (for some reasons these did not appear in Extension Manager where I first tried disabling Ethernet stuff as per the install instructions), and everything started working.

Thanks for your work on this. It's a very useful piece of software. When I get around to doing a clean install I'll post here with any interesting lessons learned, if any - but it'll probably take me a week to get around to playing with a 7.5 reinstall as I'm totally swamped with work right now.