Page cannot be displayed for topics linking to CHM

I am unable to link to individual topics of a merged chm file... that is I can get the correct topic in the TOC to be highlighted in the left pane. However, the actual topic is not displayed on the right-side pane. Instead, a page cannot be displayed error is displayed on the right-side pane. The only exception is for parent CHM file where it opens the correct topic on the right-side pane too without the page cannot be displayed error.

The merged chm is produced by Robohelp 7. Calling code is in Csharp. And, I made sure there are no '#' symbols in the path. The CHM files are on local machine and they don't have an unblock button as such. I can view them ok individually.

Code to call from csharp:

HtmlHelp(this.Handle, <<path to help file>>, HH_DISPLAY_TOC, 1292);

Any ideas if it needs another line to be added here to actually display the content in addition to the TOC?

There is another class for dealing with help: HelpProvider. You could try it.