You can't/shouldn't use OTA if your device is already jailbroken because it fails a lot of times and isn't guaranteed to work. Even if you wanted to try, evasion removes the ability to use OTA. You need to use iTunes to restore to 6.1.2. Back up your iPad before restoring just to be safe. Then use iTunes to restore to the latest firmware. Jailbreak with the latest version of evasion (currently that is 1.5) before restoring a backup (or syncing your content...not sure which method you use).