When I try and open a help file (.chm) that resides on a unc path I get the following error:
"Navigation to the webpage was canceled".
If I copy the file locally I am able to open it.
I imagine there is a security tweak to make this work.
See KB article http://support.microsoft.com/kb/892675/ which includes detailed explanation of the issue, examples and methods for deploying changes across your domain. I've copied a couple of examples below for reference.
If you want to permit opening of all CHM files in the "Intranet" zone, then the following registry entry will do the trick.
REGEDIT4 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp] [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\HHRestrictions] "MaxAllowedZone"=dword:00000001
If you want keep things more secure and only permit access to CHM files on a certain UNC path, then use the following instead replacing \\productmanuals\helpfiles with the UNC path that you want to allow (don't forget to use double backslashes)
REGEDIT4 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp] [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\HHRestrictions] "UrlAllowList"="\\\\productmanuals\\helpfiles"
See this KB article: http://support.microsoft.com/kb/896358
The answer I gave for a similar question may also apply to you - thought I would at least throw it out in case it did.