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.

For
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:\asdf.col\TFSInstall.chm
c:\documents and settings\john.coltrane\desktop\TFSInstall.chm

Solution: Move file somewhere else on your computer.

Comments

• Anonymous
  April 09, 2007
  The comment has been removed

• Anonymous
  May 06, 2008
  I don't believe it but I had my C# file in a older called C# and it didn't like the "#".  I changed it to csharp and it worked.  I don't believe it.

• Anonymous
  July 27, 2008
  Cool, my .chm file was inside a directory with name containing '#'. I removed '#' ,and now i can view .chm files.

• Anonymous
  September 03, 2008
  I didn't have the subkey ItssRestrictions in my registry, but just changing the # sign in the folder containing the .chm file fixed the issue (just like Rakesh Juyal menioned above)!

• Anonymous
  September 13, 2008
  OMG, i just had the same issue today. Taking the #s out of the directory name fixed all my C# chms! Thanks~!

• Anonymous
  October 14, 2008
  That was very very very helpful!!! Thanks a lot!!!

• Anonymous
  November 27, 2008
  ....and watch out for dots in folder names too.  My chm was on a network folder which I was referencing via a UNC path using the ip address.

• Anonymous
  November 27, 2008
  ...or maybe it is just a problem with any network share - moving the file locally meets with success.  But moving it to a UNC share using a server name rather than an IP address still had the problem. (on XP).

• Anonymous
  February 01, 2009
  It was very Help full. Thanks a lot :)

• Anonymous
  February 03, 2009
  A very helpul hint, thanks a lot!

• Anonymous
  February 05, 2009
  It was really very helpful.Thanks a lot:-)

• Anonymous
  March 05, 2009
  thanks man.. i removed the # from my file name and path and now i am able to view it.

• Anonymous
  April 10, 2009
  hey neeraj! That was very useful.Thank you so much for posting this - very useful piece of information. best wishes

• Anonymous
  June 02, 2009
  Tnxs, I had the same problem and the problem was C# in my folder name. After I renamed C# to C-sharp, everything was okay, Thank you once again for this info.

• Anonymous
  June 28, 2009
  Thanks Neeraj. It is very helpful.

• Anonymous
  July 09, 2009
  The comment has been removed

• Anonymous
  July 09, 2009
  Hi gopalmyeni, Can you send me some more details about the problem. Did you checked if there is any # character in the file or entire path? Also what error do you get when you open your chm file? Thanks, Neeraj

• Anonymous
  July 09, 2009
  The comment has been removed

• Anonymous
  July 20, 2009
  Hey, Thanks .. I created a registry and it really worked. :)

• Anonymous
  August 08, 2009
  Great! Now I can open chm files...I was wondering what on earth was the problem, now it works.

• Anonymous
  August 23, 2009
  Thanks mr Chan Chawla, I alwayse wonder y my chm file is not working on my computer, and u have a simple solution that i dont know. Thanks again.

• Anonymous
  September 04, 2009
  hi neeraj,  see the following images. i am not able to open chm files. help me.. http://i778.photobucket.com/albums/yy62/gopalmyneni/1.jpg http://i778.photobucket.com/albums/yy62/gopalmyneni/2.jpg http://i778.photobucket.com/albums/yy62/gopalmyneni/3.jpg

• Anonymous
  September 25, 2009
  It works thanks. Nice info as i have been wasting bandwidth downloading the same file again and again from different locations to see that it does not work.

• Anonymous
  September 28, 2009
  Hey Neeraj, thanks for this post. Unblocking the file property simply did the trick.

• Anonymous
  November 17, 2009
  I still can not open this file since i have the hh.exe and also set the open way and link path. It just still can not open.

• Anonymous
  November 17, 2009
  Hi Lee, I am surprised if all the above options are saturated. If the document is not very confidential, can you share that with me? Also let me know which version of OS are you using. Thanks, Neeraj

• Anonymous
  January 11, 2010
  Hi Neeraj, Removing the '#'' character from the path worked. Many thanks for your post. Cheers.

• Anonymous
  April 19, 2010
  The comment has been removed

• Anonymous
  May 12, 2010
  It worked. Thanks a lot for the useful info.

• Anonymous
  August 10, 2010
  Nice. Thanks for the reg entry pointer. Fixed my problem.

• Anonymous
  November 20, 2010
  I was going banannas with rhis error.  I have used the HTML Help Workshop for a couple of years and could not see what was wrong.  I poked around and rebuilt the project, etc., etc The problem was that I had a # in the path name.  I am using it for C# documentation so the path had the # along the way.  I changed the path name and voila! As a tip I would recommend you try the python sphinx documentor.  It will generate a Help Workshop project that you can tune from standard txt files.   It is best installed on a Linux OS.  I( never could find windows installation instructions.)  After generation you copy the directory to Windows and use the Workshop there. It saves a bunch of time. Good Luck.

• Anonymous
  December 19, 2010
  i got this nice book in .chm extension and couldn't believe it could not open..  but the first trick did it for me!!! thanks man,, all d best!!!

• Anonymous
  January 26, 2011
  That did it!  Thanks.  After several useless KBs, your registry fix was the key.

• Anonymous
  April 18, 2011
  HAHAHAHAHAHA!!! I have the best error!

1. Take any CHM file. (ANY CHM file!)
2. Copy it.
3. Create a folder with the letters ".col" in it. (note: folder can't start with period, so do something like asdf.col)
4. Put the chm file in that folder or any subfolder of it.
5. It will give you the "cannot open file" error. Example paths that will cause this error:    c:asdf.colTFSInstall.chm    c:documents and settingsjohn.coltranedesktopTFSInstall.chm

• Anonymous
  April 25, 2011
  WOW....Amazing... Thank you !! Option 1 worked for me.

• Anonymous
  December 04, 2011
  wow it's amazing,i just removed the # symbol from my folder,now its working,thx a lot guys....:)

• Anonymous
  December 15, 2011
  Your suggestion of using "unblock" really worked for me. Thanks a lot.

• Anonymous
  December 22, 2011
  It didn't work for me even after editing the registry and adding the keys. Just right click on the '.chm' file, select properties, and click on 'unblock' button!  Viola!! everything works!

• Anonymous
  September 14, 2012
  thanx friend

• Anonymous
  January 13, 2013
  'Unblock' did it for me.. Thanks dude..

• Anonymous
  March 20, 2013
  Thanks a lot... I spend 2 hours trying to figure out the reason for this..

• Anonymous
  October 18, 2014
  Thanks a lot.....it worked

• Anonymous
  April 07, 2015
  Ran into this irritating issue...thanks for the registry tip, worked a treat!

• Anonymous
  November 12, 2015
  Thanks very much. Solved the problem for me!

• Anonymous
  November 18, 2015
  Tried all option but it didn't open

• Anonymous
  February 28, 2016
  Thanks it worked for me after unblock