When attempting to open a CHM (HTML) help file from the Internet or from a network drive, the table of contents will be visible, but the content of the individual pages will show as "Action Canceled".
This symptom is caused a by a security feature in new versions of Windows. The help file is automatically marked as
potentially malicious.
There are several ways to allow the file to be opened. The preferred method is to right-click the file, and select the properties option. You will notice a button near the bottom Unblock, simply click this, and you will be able to open, and read the help file.
Another way, although not recommended unless you have many help files on a network share, is to download a utility called HHReg.exe, this can be downloaded from the www.ec-software.com website. This tool wil make the task of changing registry settings, much easier, allowing help files to be opened form selected folder, driver, URLs etc.
There is more information regarding this issue on the Microsoft website.Article ID: 13, Created On: 6/26/2010, Modified: 6/26/2010