So, as a result, the RC blocks upgrades over any build earlier than 7077. If you’ve been running the original beta (Build 7000) and you try to upgrade, you’ll see an error message.
But if you insist on doing the upgrade anyway, there’s a workaround. Start by copying the entire contents of the Windows 7 DVD to a local folder (use a bootable USB drive, or create a folder in the root of the drive you’re planning to upgrade, and then run Setup from that location).
In the folder you just created, open the Sources subfolder and then open the file Cversion.ini in a text editor like Notepad.
Change the MinClient value (highlighted in yellow above) to 7000 and save the file in the same location with the same name.
You can now run Setup without being bothered by the version check.