HTML Help from a network folder cannot be displayed

Document ID : KB000089883
Last Modified Date : 14/04/2018
Show Technical Document Details
Issue:
HTML Help from a network folder cannot be displayed
Resolution:

Symptoms

Opening an HTML Help (*.chm files) which is stored on a released network folder has the effect that no topic are displayed (under Windows).


Cause

This error occurs because Windows automatically blocks the contents of .chm files on a network folder which are opened via a UNC path (Universal Naming Convention) for reasons of security. This happens as of Windows Security Update 896358 or Windows Server 2003 Service Pack 1 which have been implemented to remove security gaps in the HTML Help.   Problems concerning the HTML Help may also occur with the security update 840315 because only files ending on *.chm are used as HTML Help files.  


Resolution

This problem requires particular specifications to be made in the Windows Registry in order to have HTML Help contents correctly displayed on a network folder.   You may either release particular URLs or a complete security zone. 

1. Releasing individual URLs:  
Individual URLs may be released in the registry path
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\ItssRestrictions
using the value "UrlAllowList".   Example:  

The network folder: \\docu\htmlhelp\uc4\ should be released.   Doing so requires the following line to be copied in a file ending on *.reg (note: it is always recommended to backup your registry before making any changes):

REGEDIT4 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp]
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\ItssRestrictions]
"UrlAllowList"="\\docu\htmlhelp\uc4\;file://\\docu\htmlhelp\uc4\"
Now execute this file.It is also possible to change the relevant value manually via the Registry Editor (Process: regedit).   Two registry entries must be added in order to release a UNC path to a network folder:
\\docu\htmlhelp\uc4\;file://\\docu\htmlhelp\uc4\    

2. Activating a security zone:  
The term zone refers to a particular network area. Windows knows 5 different security zones. The registry value "MaxAllowedZone" may be used to define the number of released zones.   The following impacts result from the values specified in "MaxAllowedZone". Default setting: 0.

0EMb0000000OKDQ.png

The Automic HTML Help is always correctly displayed when the setting MaxAllowedZone=3 has been specified.   Example:  
The registry entry "MaxAllowedZone" uses value 3.
To have this value entered in the Registry, execute a .reg file with the following line (note: it is always recommended to backup your registry before making any changes):  

REGEDIT4 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp]
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\ItssRestrictions]
"MaxAllowedZone"=dword:00000003
This setting may also be specified manually via the Registry Editor.

0EMb0000000OKDR.png

See Also:
http://support.microsoft.com/kb/896054
http://support.microsoft.com/kb/896358
http://support.microsoft.com/kb/840315
http://support.microsoft.com/kb/902225