Today saurik, the developer of the Cydia application, released a new version of the mobilesubstrate platform making it compatible with the new iOS 5. This update also gave the Dev Team the opportunity to update ultrasn0w to make it, compatible with the new iOS 5 but unfortunately it ruined the possibility to unlock using an iPhone 4 and a Gevey card. Unfortunately, the new mobilesubstrate blocks the unlock process for those who have Gevey cards, so I recommend you NOT to install the new version of mobilesubstrate and wait for Saurik to update it and solve functionality problems.
If you have already installed mobilesubstrate, uninstall it, reset your iPhone and only then try the decoding process again using Gevey.
