Visual Studio .NET help - Error 1706

[Al, Cambridge, UK]

I thought I'd share this, since it cost me 2.5 days...

When running Visual Studio .NET 2003 as a Power User, if I pressed F1
for context-sensitive help, I either (consistently for particular
highlighted keyword) got the relevant help or else visual studio would
say "Please wait while Windows configures Visual Studio .NET Enterprise
Developer 2003 - English" then grind away for a while trying to load
something (unknown) from somewhere (unknown) and eventually fail with
"Error 1706. No valid source could be found for product Visual Studio
..NET Enterprise Developer 2003 - English. The Windows installer cannot
continue."
Then when I clicked "OK", the sodding thing went off and tried to load
it all again. Twice. And then finally it would show me the correct
help, so it knew how to do it all along.

After searching fruitlessly for solutions (Q297103 is a classic "you
are in a helicopter") and re-installing twice, I worked it out by
looking inside the helpfiles. The offending help/web pages had an
ActiveX control 59CC0C20-679B-11D2-88BD-0800361A1803 to do some cookie
stuff. That classid should register C:\Program Files\Common
Files\Microsoft Shared\MSDN\CookDoc.dll so I found that file on my
system and re-registered it. Which has magically worked.

So, I hope this saves somebody else's time.
Al.