MSKB article on how to fix the viewing experience on .chm filesin reference to: Certain Web sites and HTML Help features may not work after you install security update 896358 or security update 890175 (view on Google Sidewiki)
Actually, very frustrated - followed the instructions, copied the text to the .reg file but it didn't work. Fiddled for ages, then read more MSKB articles. The article shows a UNC path to your .chm files but really the files were on my local hard drive so UNC is not appropriate. After all that reading and testing, here is text for Windows 7 .reg file - copy this into notepad, save as a .reg file and run it - I ran it from an admin account and suspected UAC and elevated security issues with Windows 7 but that was a red herring.
- c:\refs is where I put the .chm files
- I used both the C:\ and the file protocol - I think the file protocol was the one that solved it.
Windows Registry Editor Version 5.00[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x][HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\HHRestrictions]"UrlAllowList"="E:\\refs;file:///E|/refs""EnableFrameNavigationInSafeMode"=dword:00000001"MaxAllowedZone"=dword:00000003[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\ItssRestrictions]"UrlAllowList"="E:\\refs;file:///E|/refs""EnableFrameNavigationInSafeMode"=dword:00000001"MaxAllowedZone"=dword:00000003