For last couple of days, about 2 weeks after my 7.8 upgrade, lumia 900 has started to try to unlock display "automatically". Unfortunatelly it has not been able to figure out the code, so now it says "Try again in 256 minutes" after several unsuccessful tries. Quite annoying when it started last night at 3:xx am while in deep sleep and phone "peeps" for some time.
Haven't tryied reseting phone yet, wanted to ask, has anyone seen this also and would it be hardware or software related. Take phone to service or wait for a fix?
This calls for a hardware key combination reset. I'm sorry to say this deletes all personal information or content in your phone.
Nokia Lumia with Windows Phone 7
Make sure the charger is disconnected.
1. Switch the power Off.
2. Press and hold the Volume down and Camera keys.
3. Press and hold the Power key.
4. When the phone vibrates, release the power key, but continue holding the volume down and camera keys, until the phone reboots.
To answer your questions, we've encountered the same concern before. As far as we remember, it's 900 minutes on that case. The above reset is the fix for this so there's no need to bring the phone for assessment. In the event though that the above reset won't work, which is very unlikely, that's the time that you have to bring it in a Nokia Care Point. http://www.nokia.com/global/support/locations/