This should be in the FAQ section, but due to it's importance we have decided to put this on its own page.

A Windows security update patch was recently released by Microsoft which stops HTML Help (.chm) files from being viewed from across the network, or from shared or mapped drives. This also effects .chm files that are copied or emailed to and from other computers.

If you try to view a .chm file from over the network or from a network drive, you will see something similar to this:

Please note, this is not a problem with Helpmatic, it will effect all .chm files.

You will also get this problem if you email or manually copy the .chm to another computer.

More details on this patch and work arounds are detailed on the Microsoft website at, http://support.microsoft.com/kb/896358.

Downloading a .chm file (unzipped) from the internet will also have this problem. You will need to 'unblock' any downloaded .chm files by right-clicking the file, select Properties, and then click Unblock. More details on this are available at the Microsoft website here, http://support.microsoft.com/kb/902225.

We personally have found these work arounds to help somewhat solve this problem:

1. Avoid viewing .chm from network drives and avoid saving .chm files to network drives. Always work on local drives.
2. Before emailing or 'sending' someone your .chm, please zip or rar it first. You will not get a problem then.
3. .chm files that you ship with your application that get installed by an installer to end users computers will not have this problem.
   

Microsoft also have some workarounds on their website here, http://support.microsoft.com/kb/896358.