CHM table of content opens firefox/internet explorer instead of within

Windows 7 home.
I have a CHM file stored on the OS harddrive.
Whenever I try to click on the table of contents, it tries to download the htm file instead of opening it in the adjacent window. All my other chm files work normally. I'm not sure if a recent windows update did this.

Any ideas?

It sounds like the builder of the .chm was getting the page online and forgot to change the link to local.

If you really want to try to fix it, you can download this:
Download Details - Microsoft Download Center - HTML Help Workshop and Documentation

and decompile it into the html pages. If the one you need is actually there you can fix the link and recompile. May not be worth the effort if you have no desire to learn to make html help. Can you contact the author? Maybe it's been fixed or you could send a bug report.