If you were one of the brave souls that installed the leaked Froyo Release Candidate on their Nexus One and miss being able to download and install protected apps from the Market, you’re in luck — as long as you have ADB or SuperUser access.
If you have SU access on your phone, grab the froyo.zip file from XDA-Developers.com and copy it to the root of your sdcard.
From your Nexus One, open your terminal emulator and type in the following (press “enter” at the end of each line).
mount -o remount,rw /system
mv build.prop new.build.prop
mv froyo.prop build.prop
When you’ve booted up, open Dialer and type in the following code:
The sequence should disappear after you press the last *, and you should receive an update notification that says “check-in succeeded”.
Head over to the Market and your protected apps should be available again.
(For ADB instructions, head over to the article at XDA-Developers.com)