I may be wrong here, but it looks like it may not be finding your chm file. Depending on your default directory and your variable replacement.
The following works fine for me:
SET HELP on
SET HELP to alltrim(m.cHelpPath)
SET TOPIC TO alltrim(m.cHelpTopic)
HELP
SET HELP TO
where m.cHelpPath contains the full path and filename of the chm. I would definitely get rid of the &ghelp and set it to (gpath+ghelp). If you dont use your gpath then try setting a default dir first "set default"
Lots of times, things will work on one machine and not another when it's a path issue, especially if you are working on a developer machine. Developer machines seem to always find the right path.
If this doesnt work try adding a button to one of your forms and hardcode everything to your chm file.
SET HELP on
SET HELP to 'c:\mypath\mychm.chm'
SET TOPIC TO 'mytopic'
Help
SET HELP TO
this may give you some insight into whether it is an OS issue or not.