If you're getting an error on the iPad Baseband that means you have the new bootrom 3GS. Note that once you flash the iPad Baseband, you cannot downgrade it to an official baseband. On the new bootrom 3GS, you must first downgrade your device to 4.1 (does not require blobs), flash the iPad Baseband, then upgrade your iOS while preserving your new iPad Baseband, jailbreak and unlock. You can only unlock using UltraSn0w on the new bootrom 3GS on iOS 6.1 or below, meaning 6.1.2 or 6.1.3 will not work.