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2011-02-17T08:27:54Z

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Error Accessing and Displaying CHM Files, e.g. ''"The page cannot be displayed"'' error.

There are several possible reasons why CHM files are unreadable.

* The CHM viewer component is not properly registered 
<blockquote>
The system file <WINDOWS>\system32\hhctrl.ocx may be missing, corrupted, or unregistered. 
'''Solution''': Run "regsvr32 hhctrl.ocx" command from the command line to register the library in the system.
</blockquote>

* The CHM file is stored in the folder with '#' (hash) character in the path 
<blockquote>
The hash character signifies an anchor in HTML so the CHM viewer fails to resolve the path
properly and to retrieve the content. 

'''Solution''': Remove the '#' (hash) character from the directory name. 
Also avoid using '?', '&', and '+' characters in directory names.
</blockquote>

* A security update for Windows XP® may block access to CHM files
<blockquote>
Windows XP® security update blocks active content in CHM files to protect system security. 

'''Solution''': Run Windows Explorer, right-click on the CHM file, and select Properties from the
popup menu. Click on the Unblock button (below the Advanced button on the General
page). Click Apply to show the content. Once the CHM file has been unblocked, the Unblock
button disappears.
</blockquote>

* The CHM file is in the restricted Internet zone
<blockquote>
When a CHM file is stored remotely, e.g. on the network drive or on a remote server,
a ''"The page cannot be displayed"'' error may occur. If the associated security zone
is restricted, then CHM files won't be displayed as well. 

'''Solution''': Modify the '''ItssRestrictions''' registry entry to enable a specific security zone. 
Follow these steps: 
</blockquote>
:# Run 'regedit' command from the command line.
:# Locate and then click the following subkey:
:#: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\ItssRestrictions
:#: Note: If this registry subkey does not exist, then create it.
:# Right-click the ItssRestrictions subkey, point to New, and then click DWORD Value.
:# Type MaxAllowedZone, and then press ENTER.
:# Right-click the MaxAllowedZone value, and then click Modify.
:# In the Value data box, type a number from 0 and 4, and then click OK.
:#: The values settings are
:#: 0 = My Computer
:#: 1 = Local Intranet Zone
:#: 2 = Trusted sites Zone
:#: 3 = Internet Zone
:#: 4 = Restricted Sites Zone
:#: For most CHM files, the value of 1 should be enough to allow use without opening up
:#: access from/to remote CHM files in email/internet locations.
:# Quit Registry Editor.

<blockquote>
{{Warning| Enable only those security zones that you trust. Do not enable security zones about which you are not sure.}}
</blockquote>
<blockquote>
More information: [http://support.microsoft.com/?scid=kb%3Ben-us%3B896054&x=10&y=8 www.microsoft.com]
</blockquote>

* HTML restrictions caused by certain security updates
** Certain kinds of Web-based programs may not work correctly. For example, a table of contents in HTML Help may no longer work.
** Certain HTML Help features may not work when you open a .chm file from a remote location. For example, the Related Topics feature may not work.
<blockquote>

'''Solution''': Modify the '''HHRestrictions''' registry entry to enable a specific security zone. 
Follow these steps: 
</blockquote>
:# Run 'regedit' command from the command line.
:# Locate and then click the following subkey:
:#: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\HHRestrictions
:#: Note: If this registry subkey does not exist, then create it.
:# Right-click the HHRestrictions subkey, point to New, and then click DWORD Value.
:# Type MaxAllowedZone, and then press ENTER.
:# Right-click the MaxAllowedZone value, and then click Modify.
:# In the Value data box, type a number from 0 and 4, and then click OK.
:#: The values settings are
:#: 0 = My Computer
:#: 1 = Local Intranet Zone
:#: 2 = Trusted sites Zone
:#: 3 = Internet Zone
:#: 4 = Restricted Sites Zone
:#: For most CHM files, the value of 1 should be enough to allow use without opening up
:#: access from/to remote CHM files in email/internet locations.
:# Right-click the HHRestrictions subkey, point to New, and then click DWORD Value.
:# Type EnableFrameNavigationInSafeMode, and then press ENTER.
:# Right-click the MaxAllowedZone value, and then click Modify.
:# In the Value data box, type 1 then click OK.
:# Quit Registry Editor.

<blockquote>
{{Warning| Enable only those security zones that you trust. Do not enable security zones about which you are not sure.}}
</blockquote>
<blockquote>
More information: [http://support.microsoft.com/?scid=kb%3Ben-us%3B892675&x=13&y=15 www.microsoft.com]
</blockquote>

[[category:Other Software]]

CHM files not displayed - Revision history

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