Thanks for your reply, Peter.
My tester was using:
OS X 10.4.11
But the Help didn't open when she clicked the Help button in the app.
However, when she went to the url (the Help's location on our server), it opened perfectly.
Is there something I should be doing specifically for Help that goes to a Mac?
Shouldn't I be able to generate as WebHelp and have it work properly on both Windows and Mac?
I'll go back to my developer and ask him to look closer.
Also, I just found that, of the two projects I'm doing WebHelp for, one works and one doesn't (this is specifically on a Mac).
The one that works is called from a Web application.
The one that doesn't is called from a downloadable Java application.
Again, thanks for your help.