Sometimes when you create a CHM help file, you can face some of the known issues such as the topic content blocked by Windows security policy, not working Search capability, or improperly working keyword Index in the HTML Help viewer program.
Below you will find a description of these CHM help file-related issues and their possible solutions.
If you have downloaded a CHM help file, or are trying to access such a file from a remote PC, you can find out that the HTML Help viewer application displays only the Table of Contents in the left side, but instead of the topic content in the right side you will see a message saying "Navigation to the webpage was canceled" or "This program cannot display the webpage".
Now if you open the help file, the content of help topics should be properly displayed. Of course, you should unblock CHM files only if you trust to the source from where you received it.
Another issue that you can face with a CHM help file that you have compiled using a help authoring tool is the Search tab that does not find any help topics even if you type keywords that actually exist in the content.
To solve this issue, you can try to re-install MS HTML Help Workshop package as explained below:
Now the Search capability should work properly.
In addition, if you have found that the keywords on the Index tab in your CHM file are not sorted alphabetically, or the keywords which are associated with more than one topic do not display the actual topic titles (for example, Untitled name is shown for each topic), you can also solve the issue by re-installing MS HTML Help Workshop package and re-compiling your help file.
Finally, if you still cannot open your CHM file or it is working or displayed incorrectly, ensure that the path to the file location (including the names of containing folders and the name of the CHM file itself), does not contain the characters such as "_", "#", and also that it does not contain national characters.
This is a known error that may also prevent a CHM file from working properly, so it is recommended to avoid unallowed characters, and to use Latin characters only for the help file's name and for the containing folders.
You can download one of the recommendable help authoring tools that combines a rich feature-set, slight learning curve, and affordable price.