Ever wondered why your .CHM file(s) does not work?


I had couple
of .CHM files, specially for C# .NET related stuff and I saw some of the chm
files when I open them I see "This page cannot be displayed" error.
Finally I figured out that there could be two reasons for this:

[Option 1
courtesy chan.chawla from the posted comment, adding as the first option to be
tried out before going any further]

1. Double
click the .chm file. It will open a security dialog. Uncheck "Always ask
after opening this file". Alternatively, right click on the file you want
to open, click Properties and then click Unblock. This should do the trick.

2. If you chm
file name or the path contains '#' character, just get rid of that and I guess
you would be able to start viewing your chm files again.

3. If nothing
works, try this.

Because of a
Microsoft Service Pack, the chm files does not have enough permissions (by
default). This case is usually when you try to open .chm files over network.
The resolution for this is as follows:

  • Click Start, click Run, type regedit, and
    then click OK.
  • Locate and then click the following
    subkey: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\ItssRestrictions[If this registry subkey does not exist, 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 1, and then
    click OK.
  • Quit Registry Editor.

more information check https://support.microsoft.com/kb/896358.

4. One more reason provided for unable to open chm files [courtesy colin.cole]

Any chm file that is in a folder named *.col* will not open.
Example paths that will cause this error:
c:\documents and settings\john.coltrane\desktop\TFSInstall.chm

Solution: Move file somewhere else on your computer.