Saurik has released updated Corona for untethered jailbreak through Cydia, which includes fixes for iBooks and launch issues.
How to Install Corona
“Corona (5.0.1 untether) 1.0-4 is now out: users of redsn0w or the older packages should install. This fixes both iBooks and launchd (again).”
It is recommended for owners of jailbroken A4 devices to install the latest Corona package on their devices via Cydia.