To fix errors related to iBooks app after untethered iOS 5.0.1 jailbreak with RedSn0w 0.9.10b3, Dev Team has released now RedSn0w 0.9.10b4 for Windows and Mac users.
See also:
Corona Jailbreak for iOS 5.0.1 Updated to Fix iBooks
How to Do Untethered Jailbreak of iOS 5.0.1 with PwnageTool 5.0.1
Sn0wBreeze v2.9 Untethered Jailbreak Available Now
Download RedSn0w 0.9.10b4 for Windows
Download RedSn0w 0.9.10b4 for Mac