"You can’t upgrade this prerelease version of Windows 7. Go online to see how to install Windows 7 and keep your files and settings."
This is the solution from Microsft's Blog...http://blogs.msdn.com/e7/archive/2009/04/07/delivering-a-quality-upgrade-experience.aspx
Here’s what you can do to bypass the check for pre-release upgrade IF YOU REALLY REALLY NEED TO:
- Download the ISO as you did previously and burn the ISO to a DVD.
- Copy the whole image to a storage location you wish to run the upgrade from (a bootable flash drive or a directory on any partition on the machine running the pre-release build).
- Browse to the sources directory.
- Open the file cversion.ini in a text editor like Notepad.
- Modify the MinClient build number to a value lower than the down-level build. For example, change 7100 to 7000
- Save the file in place with the same name.
- Run setup like you would normally from this modified copy of the image and the version check will be bypassed.