Unable to open .chm HTML Help files

Couple of times we find it difficult to open HTML help file and when we open topics in the .chm file cannot be viewed and it is because of getting blocked and all you have to do is to unblock the file and this time you can see the contents :-)

Steps to Unblock is:
1. Right-click the CHM file, and then click Properties.
2.Click Unblock.
3.Double-click the .chm file to open the file.
More information is available in the KB article - http://support.microsoft.com/kb/902225/EN-US/