CHM file won't show correctly

I've had problems on my Windows XP machine viewing html help files with the *.chm extension. Also it only happened on files that I downloaded from the internet. When opened, the file has the tree structure on the left and in the right-hand pane says "Action Cancelled"
To resolve this issue, right click on the filename or icon and choose "Properties." Under the general tab you will see a section called "Security" under the "Attributes" section. Click on "Unblock." Now you should be able to open up the file.

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