Stefan Krueger emailed me asking if I had problems viewing the new MSI.chm. To be honest I hadn't even looked at it yet ( despite my moaning earlier this year about not having access to to it ) because I've been so swamped with recent changes at work and the struggle my wife is going through.
After finally downloading the file and testing it on a clean virtual machine, I stumbled onto the fact that the CHM wouldn't work from a UNC path but that it would work when I copied it locally.
So I did some searching and I found a KB article from Microsoft pointing in the direction of a change to CHM behavior in security bulletin MS05-026.
I had never noticed this behavior before. I love learning something new every day. Now off to read the MSI.CHM and learn a few more new things.