iPhone Hacking Community released iOS 5.0.1 untethered jailbreak last month which can jailbreak all A4 based and older devices. Pod2g, who developed 5.0.1 untether jailbreak, is still working to bring an untethered jailbreak to newer devices i.e., iPhone 4S and iPad 2.
As we know untethered jailbreak breaks the Apple restrictions and allows us to install any third-party app and tweak, but it also contains some bugs. The current iOS 5.0.1 untehered jailbreak causes iBooks and some other apps to crash on launch.
Cororna 1.0-5 tweak available through Cydia store not only converts the tethered jailbreak into untethered but this time also fixes the iBooks and crashing of other apps.
If you have already jailbroken your device with Redsn0w, you can safely install the latest release of Corona on your device to fix the iBooks issues. For this purpose launch Cydia, go to Changes tab and tap the Refresh button on top. After the repos are refreshed, search for Corona and install it.