Monday, May 26, 2008

Unable to view .CHM files - Action canceled

If you found you are unable to open .CHM files stored on the network, showing an Action canceled error as per below screenshot, then it's very likely you have installed Microsoft Security Update 896358 that's preventing from opening .CHM stored on the network or downloaded from Internet.

See Microsoft KB 892675 for details on how to enable it back and keep a certain security level per your liking (MaxAllowedZone = 2 was just enough for me).

Update 28 October 2008 - thanks to Kadir Rahman

Before making any changes to the registry, check the .chm file properties and use the Unlock button if there is one. In my case I didn't have it and the .chm was part of the help reference of a network application I couldn't copy locally so I had to go for the registry change.

Update 08 October 2011

You can also use HHReg - HTML Help Registration Utility to make the registry changes for you.


  1. Don't simply change your security level. If the file was copied from other computer/internet, right click on the file and select properties. Click on unblock button at the very bottom of general tab.

  2. Thanks for the suggestion Kadir, I've seen that before although the button doesn't seem to be always available.