Hello folks I have a iOS blog in a non English language and its the only iOS blog in my language, so alot of people expect from me to post tutorials on Jailbreaking , unlock...etc I had posted a video on how to downgrade the iOS firmware , and I got a lot of comments from viewers who had encountered some errors while trying to restore specially when trying to restore from 4.3.5 to 4.3.3 I decided to do a little research on the net and make a video tutorial for my views to fix those issues, I came across different blogs and video's with different solution. I first checked apple's support page to find out about the main cause of the errors and then find a solution ( http://support.apple.com/kb/TS3694) These are the results I came to in the End , please correct me if they are wrong or if you have anything else please add it in a comment( and I have a few questions which I didn't get any answers for ): 1) Error 20: Cause (These errors typically occur when security software interferes with the restore and update process) Fix: Temporary disable any firewall until you finish the restore 2) The most common error 3194 Cause : a) Don't have Shsh Blobs b) iTunes is not directed those blobs Fix: you can't fix (a) b) if you restore to the latest iOS stock firmware uncheck the option " Set hosts to Cydia on Exit" in TinyUmbrella If you are restoring to an older firmware Check that option and it modifies you host files and redirects iTunes to Saurik's server instead of apple's. Error 1013: Cause : These errors may be the result of the connection to gs.apple.com being redirected or blocked Fix : open the host files and put a # symbol infrot of the cydia IP so it gets ignored. But if we delete or ignore the IP of cydia , doesn't that cause error 3194 in the first place? Error 1015: Cause : This error is typically caused by attempts to downgrade the iPhone, iPad, or iPod touch's software. This can occur when you attempt to restore using an older .ipsw file. Downgrading to a previous version is not supported. To resolve this issue, attempt to restore with the latest iPhone, iPad, or iPod touch software available from Apple. This error can also occur when an unauthorized modification of the iOS has occurred and you are now trying to restore to an authorized, default state. Very rarely this error is caused by a hardware issue and requires service. Fix: use RecBoot or Fix Recovery ( what is the different between these two? and if there any difference between Fix Recovery and kick device of out of recovery button in TU? ) Error 1600 , 1601 Fix : Uninstall and reinstall the latest version of iTunes Error 1602 : Fix : Ensure proper USB isolation troubleshooting has been performed, and test with a known-good cable. Follow the steps listed for Error 1604. This error may be resolved by disabling, deactivating, or uninstalling third-party security, antivirus, and firewall software. See steps in this article for details on troubleshooting security software. Error 1604 : This error is often related to USB timing. Try changing USB ports, uninstalling and reinstalling USB ports, and other available USB troubleshooting steps (troubleshooting USB connections, device not recognized properly, computer won't recognize a FireWire or USB device). If you are using a dock, bypass it and connect directly to the white Apple USB dock connector cable. If the issue persists on a known-good computer, the device may need service. If the issue is not resolved by USB isolation troubleshooting, and another computer is not available, try these steps to resolve the issue: Connect the device to iTunes, confirm that the device is in Recovery Mode. If it's not in Recovery Mode, put it into Recovery Mode. Restore and wait for error 1604. When prompted, click OK. Close and reopen iTunes while iPhone remains connected. iPhone should now be recognized in Recovery Mode again. Try to restore again. If the steps above do not resolve the issue, try restoring using a known-good USB cable, computer, and network connection. Thanks in advance for your input and please post cause and fix of any other common error while downgrading which I forgot to mention , and apologize if my English is not good.