- Erasing devices with very old iOS version. It isn't possible to erase iOS devices if the iOS version on the device is very old (for example iOS 4). The result is the same if you try to upgrade the software using iTunes (you get "error 9"). This problem has surfaced with iOS 9, but there is no far no fix from Apple. If the device has really old iOS version, it is recommended to upgrade the software version from device settings (Settings > General > Software Update) before erasing with B5M.
- Erasing devices where original HW components have been replaced by 3rd party components. If HW components of the device have been replaced by 3rd party components, it will not be possible to erase the device with B5M. In this case the erasure failed reason in B5M user interface and in erasure report will be "Failed with error 53". Software update will also fail if you try the upgrade from device settings or using iTunes (you get "error 53"). The most common case is that a broken home button has been replaced by a 3rd party button. Apple has fixed "error 53" in iOS 9.3: https://support.apple.com/en-us/HT205628