"Action Cancelled" or "Page Cannot Be Displayed" when viewing a CHM file

[Jamie Edwards]

Registration for HTML Help files is required since Microsoft issued a security patch for Microsoft Internet Explorer, disabling in general all HTML Help files that are viewed from a network drive.

http://www.ec-software.com/products_hhreg.html

How to fix it? There are several ways to fix this problem. The first (and this is the way recommended by Microsoft) is: put the CHM files onto the local harddrive. Files viewed from local drives are not affected.
If this is not possible or not desirable, you can explicitly register individual help files and folders to allow viewing them over the network or edit the Windows registry to make the security settings less strict in general. Microsoft describes the necessary steps in detail in this knowledgebase article KB 896054.

HHReg helps you with the registry editing task. Modifying the Windows registry is tedious and error-prone. HHReg provides a simple user interface to view and modify the list of registered HTML Help files and folders.