I've forwarded this to our Installer Support team, and hope to have an answer for you soon.
We're not sure why you're seeing this, but the Answer Man says to copy the contents of the DMG volume to a folder on your desktop, and run it from there.
Let us know whether this works in your case.
Hi, thanks for the quick response, copying the DMG files into a new folder on my desktop seemed to do the trick! Installed perfectly from there. Thanks for the help.