Fix: Cannot View CHM Files from a Network Drive in
Windows XP/2003/Vista
When you open a .CHM file over a
network drive in a Windows XP/2003/Vista computer, the right pane may show the
following message instead of displaying the topic/contents.
Navigation to the webpage was
canceled
This is perfectly normal, as
Microsoft Security Updates 896358 & 840315 block display of CHM file
contents when opened from a network drive. And in Windows Vista, the security
update is included by default. Microsoft issues workarounds (registry edits)
for this problem in article KB896054.
It documents the following methods to enable CHM functionality from a network
drive.
- How to use UrlAllowList to enable specific URLs
- How to use the MaxAllowedZone value to enable a security zone
- How to use both UrlAllowList and the MaxAllowedZone value
- Use NestedProtocolList to enable nested protocols within a URL
Related Tip: For downloaded CHM files which are stored in the local hard drive,
right-click the CHM file, and then click Properties. Click Unblock.
Double-click the CHM file to view the contents.
HHReg
Utility Automates the Task
HHReg (HTML Help Registration Utility) automates the steps in KB896054.
It allows you register your individual .CHM files or the folders containing
your .CHM files, so that it does not compromise security. HHReg works fine in
Windows Vista as well.
Start HHReg and add the CHM file by
clicking Add File. To add a network folder which contains CHM files, use
the Add Folder button, Browse and add the UNC path.
You should now be able to view CHM
contents from the network share.
The setting will be stored in the
following registry keys, in a String value named UrlAllowList:
HKEY_LOCAL_MACHINE SOFTWARE
Microsoft HTMLHelp 1.x ItssRestrictions
and
HKEY_LOCAL_MACHINE SOFTWARE
Microsoft HTMLHelp 1.x HHRestrictions
Additional
Information
If you want to configure the
MaxAllowedZone value to enable a security zone as per Example 2 in KB896054,
use the General Security tab in HHReg.
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