>>Once you upgrade, there's no way to downgrade to an earlier iOS version.
As I suspected.
>>If it was a software error built into the latest upgrade, everybody would have the problem.
Yes, but that assumes that everyone started the upgrade from the same point -a legit IOS version.
I still wonder about whether a jailbreak may be behind this. I found the following link at
https://discussions.apple.com/thread/5028846
The title is 'Help please my ipad has been jailbroken'
First text reads: How do i reset my ipad it appears that my ipad has been jailbroken without my knowledge according to the Lookout antivirus software? iPad, iOS 5.1.1
A solution that apparently worked is posted as:-
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This solved my question by
Demo on May 12, 2013 6:01 AM
Try recovery mode. This will totally erase the device, which is what you need to do anyway.
You can read about it here or just follow the instructions below, copied from the support article.
http://support.apple.com/kb/ht4097
Recovery Mode Instructions
- Disconnect the USB cable from the iPad, but leave the other end of the cable connected to your computer's USB port.
- Turn off iPad: Press and hold the Sleep/Wake button for a few seconds until the red slider appears, then slide the slider. Wait for iPad to turn off.
- If you cannot turn off iPad using the slider, press and hold the Sleep/Wake and Home buttons at the same time. When the iPad turns off, release the Sleep/Wake and Home buttons.
- While pressing and holding the Home button, reconnect the USB cable to iPad. When you reconnect the USB cable, iPad should power on.
- Continue holding the Home button until you see the "Connect to iTunes" screen. When this screen appears you can release the Home button.
- If necessary, open iTunes. You should see the recovery mode alert that iTunes has detected an iPad in recovery mode.
- Use iTunes to restore iPad.
See the answer in context
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In the same topic someone else posted 'Put it in DFU mode (Recovery may not on occasion completely clear a jailbreak, use Google for instructions on how to do it) and then Restore it as a new device in iTunes.'
I hope that this is some help. (If you try the above, don't forget that all data will be lost, so save anything beforehand.)