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Cannot open Compiled HTML .chm on Vista

I have just tried to open a file with a .chm extension on a computer running Windows Vista. The file is located on my desktop yet when I tried to open it only the table of contents would display and not the actual pages containing any content. Instead I was presented with a screen that said: 'Navigation to the webpage was cancelled'.


I have seen issues before on Windows XP machines where I couldn't open or run compiled HTML .chm from a network share (.chm files would fail to display any content in the same fashion as this problem was.) The only differences in this case being the file was local, it was on my desktop on my Vista computer!

After eventually right clicking the .chm file and checking properties I noticed an option at the bottom of the 'General' tab:


The option explained that "This file came from another computer and might be blocked to help protect this computer."

Since I had downloaded this help file from Microsoft's website I knew it could be trusted and clicked on the 'unblock' button. After which I could open the file as per normal and it displayed both the table of contents and all of the information/content.

Note - files with a .chm extension could potentially execute commands on your computer leaving you subject to malicious attack. If the .chm file is untrusted you shouldn't click the unblock button and open the file.

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