My guess would be that you have not applied patch 802. See Opening Projects on my site. 802 is a critical update and how to fix the damage done by not applying it is covered in that article.
I will shortly be moving this post to the RoboHelp HTML forum as this forum is for problems with HTML Help - as in CHMs.That may break the link to this thread as we are not sure if a forum problem has been fixed. I will wait until you confirm you have seen this reply, then the thread will move to http://forums.adobe.com/community/robohelp/robohelp_html
See www.grainge.org for RoboHelp and Authoring tips
Thank you for the response. I will go through the topic that you have recommended
and try the fix.
Yes, It worked. I followed your instructions and installed the required updates and the issue was fixed.
Thank you so much for your help.