Questions similar to this have been posted on the Bentley Discussion Groups and elsewhere.

Q  Windows HTML Help displays an empty panel when I open a help (.chm) file located on our network. How do I view an HTML Help file over a network?

A  This problem was introduced by one of Microsoft's security updates for Windows. HTML Help files are potentially unsafe, from the Internet point of view, because they may carry more than just help information. It's possible to include malicious executable code in an HTML Help file. The security fix prevents you from downloading a HTML Help file with potentially dangerous content over the Internet. It also prevents you from downloading perfectly harmless HTML Help files as well.

Unfortunately, the Microsoft fix doesn't differentiate between the Internet and your own local area network (Intranet). As a result, you are prevented from reading an HTML Help file even when it's located in your own office on any computer other than your own. When you try to open a help file, the contents tree in the left panel may be visible, but the useful content in the right panel is invisible.

A simple but flawed solution is to copy the .chm file to your own computer. The flaws in this approach are …

• Any Windows shortcut to the help file is invalidated (you need to shortcuts manually)
• If the server version of the help file is subsequently updated, your local copy becomes out of date

If you want to view .chm files over your network, there are several solutions proposed in this Microsoft knowledge base article. One of the simplest approaches is to edit the Windows Registry.

WARNING: Editing the registry may cause your system to become unstable or unusable… always proceed with caution and check with your system administrator.

To modify the ItssRestrictions registry entry to enable a specific security zone, follow these steps …

1. Click Start, select Run, type RegEdit, and then Enter.
2. Locate the following key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\ItssRestrictions (Note: If this key does not exist, create it by pointing to Edit|New|Key and then entering ItssRestrictions and then Enter).
3. Right-click the ItssRestrictions key, point to Edit|New|WORD Value, then type MaxAllowedZone and press Enter.
4. Right-click the MaxAllowedZone value, and then click Modify.
5. In the Value data box, type a number from 0 and 4, then Enter.
6. Quit RegEdit.

Valid values for MaxAllowedZone

MaxAllowedZone	Local Machine	Local Intranet	Trusted Sites	Internet	Restricted Sites
0	Allowed	Blocked	Blocked	Blocked	Blocked
1	Allowed	Allowed	Blocked	Blocked	Blocked
2	Allowed	Allowed	Allowed	Blocked	Blocked
3	Allowed	Allowed	Allowed	Allowed	Blocked
4	Allowed	Allowed	Allowed	Allowed	Allowed

You need to set MaxAllowedZone to 1 to view HTML Help files on an Intranet location. Microsoft recommends that you don't set the value higher than 1. With this change in place, you should be able to read help properly.

You can read more about this and other solutions in this Microsoft knowledge base article.