Nothing to see here

There are plenty of solutions on the web about unblocking chm files in Vista etc but here is a curly one that can catch you out – if the path or file name of the .chm contains the “#” character then you have a problem. The solution is to rename it, removing the # character.

See http://support.microsoft.com/kb/319247 for details.

I hope this saves you the considerable amount of time it took me to find this.