If you’re getting “Navigation to the webpage was canceled” error while opening CHM files in Windows 7, you shouldn’t blame Windows for that, because Microsoft by default includes a security patch to block CHM files on network drives or comes from other computers in Windows, these Compiled Help files can contain scripts that can harm your Computer, hence you can’t view any help topics or CHM Viewer won’t display any, here is how to fix this error.
First, make sure you’ve saved CHM file locally to your computer, simply downloading the file from the browser and clicking open from dialog box will give you the errors mentioned above.
1.. Right click on the CHM file you’ve saved earlier, select “Properties” on the General tab and click “Unblock” button.
2. Sometimes unregistered HTML Help viewer component can also cause this problem, try to register it by running the command in command prompt “regsvr32 hhctrl.ocx”.
3. Doesn’t get simpler than this, than editing registry, download and run the portable HHreg file, which explicitly permits specified added CHM files and folders in the registry. All you need to do is manually add those CHM files which you’re were not able to access or displayed correctly in the CHM viewer.