Some .CHM files may not render properly on Windows Vista and Windows 7

This article provides the steps for fixing the issue that some .CHM files do not render properly.

Applies to:   Windows 7 Service Pack 1
Original KB number:   2021383


When attempting to open a Compiled HTML Help (.CHM) file on Windows Vista or Windows 7, the file may open but display one of the following messages instead of the expected content:

  • Navigation to the webpage was canceled.

  • Action canceled.


This will occur if the .CHM file has been flagged as downloaded from an untrusted source, such as the Internet.


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 labeled Unblock.
  3. Click OK.

More information

This behavior is a function of the Attachment Manager, which applies a Zone Identifier to files downloaded from any source that is considered untrusted or at risk, such as the Internet Zone.