Just recently, the Dev Team released beta 3 of RedSn0w for Mac and Windows. This new update fixes an error that causes MobileSubstrate to sometimes crash on jailbroken devices. This error apparently only happened when RedSn0w was running over an existing jailbreak.
You can download the latest RedSn0w from our downloads page.
Update #3: The b3 version of redsn0w fixes a problem where re-running redsn0w over an existing jailbreak would cause MobileSubstrate-based apps to stop running until MS was installed again. Now you can re-run the redsn0w jailbreak step without worrying about that (but still remember to de-select the “Install Cydia” option if it’s already installed).TIP: If auto-detection fails and redsn0w tells you no identifying data was found, you can always pre-select theappropriate 5.0.1 IPSW using “Extras->Select IPSW”.