Robohelp 8 won't display PDFs in Windows 7

Hi,

I am having trouble with a .chm project that was created for Windows XP use that now needs to work with Windows7. I have tested the functionality of the project and everything but the PDFs works properly. It gives me a blank screen with an x in the corner. When the URL is copied into a new window, it works fine. Is there anything I can do to resolve this?