Some .CHM files may not render properly on Windows XP, Windows Vista, Windows 7, Windows 8.1, Windows 10 and Windows 11.

When attempting to open a Compiled HTML Help (.CHM) file, the file may open but display one of the following messages instead of the expected content:

  * Navigation to the web page was cancelled.
  * Action cancelled.
	
To resolve this issue, carry out the following steps:

  1. Right-click the .CHM file and choose Properties
  2. On the General tab, click the button labelled "Unblock"
  3. Click OK

For further information in this issue, refer to the following Microsoft articles.   

For Windows XP
http://support.microsoft.com/kb/902225

For Windows Vista and Windows 7
http://support.microsoft.com/kb/2021383