WinPwn 2.5 Beta 2 has been released to fix an error with IPSW creation and QuickPwn.
This update fixes a WinPwn bug which caused the application to crash when building an IPSW for a 2G iPhone. It also fixes a QuickPwn crash bug.
You can download the updated version of WinPwn here
NOTE*: You can also use the update feature in WinPwn to get the latest version.