First thing to check is whether you get this problem only in this project or any project. Create a new test project with just a couple of topics or open a sample project.
Click Open on the RoboHelp Starter page and then click Samples in the ribbon on the left.
See www.grainge.org for RoboHelp and Authoring tips
It's just this project.
OK, Peter my friend, stop the presses. I made some corrections to some broken links and voila! I can compile again.
I have to go to a meeting now but will post if I am missing something. Will compile as I am at the meeting.
Everything seems to be fine now. I just fixed a few of these links (there are only 20 broken links).