Fairly new to RH, I am experiencing this recreating old Win help files which we have lost the source files for. I managed to work round this by coding the special characters. Really tedious. Hoping there is a simpler solution.
None I know of, as above. I assume you are just trying to recreate the source files and not generate winhelp. Nobody uses it now and it will not run on any modern OS.
See www.grainge.org for free RoboHelp and Authoring information.
I've experienced this problem in a different context. It's actually caused by an incompatible file encoding.
If you're a Mac user you can use these instructions for changing the file encoding (I had to change to ANSI encoding, but you might need to change to UTF-8).
If you're a Windows user, you need an advanced text editor like Notepad++ to be able to change the encoding.