RoboHelp for Word Version 8-Run-time error 49-Bad DLL calling convention

I just installed the trial version of RH8. I have RH5 installed. I also have Word97 installed. When I start RH8, the RH Explorer pane opens, but when it tries to open Word, the following error message appears: "Microsoft Visual Basic - Run-time error '49'. Bad DLL calling convention." Any ideas on what I can do to fix this problem?