I believe this is caused by background WiFi usage. Try to turn off any automatic updates or syncs.
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Finally got the 20150319 update installed.
For those who can't do OTA and got the "Your system was damaged, wireless update is disabled" error, you could try this:
- Download the update from needrom here
http://www.needrom.com/download/jiayu-s3/
- Extract the file and get the update.zip, do not extract the update.zip
- Copy the update.zip to SD card on phone directory
- Run wireless update (from settings > about phone) and open options. Select Local updates.
- Select the update.zip and select update now.
Or you can boot into recovery and install the update from there
The update will not erase your apps and data.
Variety unlock and Font manager is removed.
Warning: after the update, if the phone has custom recovery, it will be erased and you'll need to re-install it.
Google service might force closed. If it does, just re-flash it using recovery (it's handy to keep gapps installer in the phone)