About a week ago, the Chronic Dev Team released an updated version of its untethered jailbreak for iOS 4.2.1, dubbed greenpois0n Release Candidate 6. While the jailbreak proved to be pretty stable, the latest version of iBooks would not work properly once the jailbreak was applied.
The issue is not directly related to the jailbreak, as Apple released an updated version of iBooks able to detect jailbroken devices around the time greenpois0n RC6 launched. As a result, iBooks refused to work with all jailbreaks – including greenpois0n (click here for more details).
The new version, called Release Candidate 6.1, includes a piece of code put together by hacker comex, designed to circumvent the iBooks jailbreak detection mechanism, and the update now allows users to use iBooks without any hiccups.
The jailbreak comes in two flavors, Mac and Windows, and is compatible with iPad, iPhone 3GS, fourth generation iPhone and iPod touch, and second generation Apple TV running iOS 4.2.1.
As usual, remember that jailbreaking your iPad is legal, as long as you do not install/use copyrighted content obtained illegally.