.chm Help Files Open With an Error or are Blank

Issue Details

• I have downloaded NI's CHM Help files or CHMs in a ZIP file. When I open the CHM file, all the topics and tree structure is visible, but the pages are blank. Is there a local security policy that I am unaware of?
• Whenever I open a .chm help file, I get one of the following page loading errors:

Navigation to the webpage was canceled 

The address is not valid

 

 

Solution

This problem can occur because the file has been blocked by your security or anti-virus software. Certain versions of Microsoft Windows will automatically block .chm files as a security measure.

If you're certain that the .chm help files come from a trusted source, follow the steps below to unblock a particular file and resolve the issue:

1. Right-click on the .chm help file in Windows File Explorer and select Properties.

2. At the bottom of the General Properties pane, click Unblock, then click Apply.
   • If this option is not visible, the file is likely already unblocked, not marked as a downloaded from the internet, or blocked by higher-level security policies. Skip to step 3 instead.

3. If the Unblock option was not visible in step 2, use the Unblock-File PowerShell command to unblock the file instead.
   1. From the Windows Start Menu, search for PowerShell.
   2. Right-click it and select Run as administrator.

1. 3. Enter Unblock-File -Path "<File Location>" where <File Location> is replaced with the path to your .chm file.

4. Repeat the unblocking procedure for all .chm files you wish to open.

Additional Information

• These issues can also occur when opening the .chm file from a .zip file that has not been unzipped and saved on your computer. If your .chm file is part of a zipped file or folder, unzip it before attempting to open the .chm file.
• Another reason behind this behavior is if the .chm files are moved from their original location. If this is the case, place them back to their original location. Create a local copy of the .chm file on your C:\ drive if one does not already exist.