When I press F1 inside RoboHTML or select Help | Index, the
.chm rarely opens anymore. The program seems to think about, but
then decides it's not worth the effort. So, instead, I usually have
to go and manually double-click on the .chm file inside the install
directory using Windows Explorer.
Are you certain it's looking for the .CHM? I'd be looking at
Tools > Options... > General tab and ensuring the "Use
Offline Help" hasn't been DE-selected, forcing RoboHelp to look at
the internet for its help.