I don't know if anyone can shed light on this, but all See
Also buttons in all the CHM help files (both my own and those
associated with the software I use) stopped working some moths ago.
All that's left is a an 'X' where the See Also button used to be in
the compiled output.
The fact that every single CHM file seems to have this
problem (including Robohelps own CHM help files) and not just ones
I produce suggests the problem lies outside Robohelp.
I've tried on computers using varying antvirus programs
(Panda, MacAfee, etc) and that's not the problem.
I'm beginning to wonder in one of the many security patches
from Microsoft is interfering with the See Also button.
It sounds like something has unregistered your copy of the
HTML Help ActiveX control (%windir%\system32\hhctrl.ocx).
POSTSCRIPT: This may be an issue where you first need to
unregister the HTML Help ActiveX control before you re-register it.
To do this, open a Command Prompt window and then run the following