Ive answered my own query! I went through the entire system, removing
all invalid uninstallers, Algorithmix files, Audiograbber files, registry entries referencing algo*, registry entries referencing Audiograbber, start menu entries etc - to make sure that it looked as if Audiograbber and Algorithmix had never been installed at all! Then I did a clean re-install of Audiograbber, followed by the Lame encoder and then the Algorithmix plug-ins. All went OK and now 100% again.
The noticed difference with the Algorithmix installer is that the first plug-in asked for an install path this time, whereas before this dialog was never presented - so I conclude that some remnant of a previous invalid installation was causing the problem!
