The iPhone Dev Team has released PwnageTool 4.1.2 update for iOS 4.1. This update includes a bug fix for Mac OS X 10.5.x Leopard users.
According to iPhone Team:
“You only need to run PwnageTool 4.1.2 version if you’re at OS X 10.5.x and were seeing Cydia errors.”
Download PwnageTool 4.1.2
Download iOS 4.1
Download iTunes for Windows and Mac