He set phone encryption in settings and process has been interrupted or there was some errors while encrypting.
This procedure takes a while, even few houers. If phone will be rebooted by user or by power loss (weak battery) encrypion will fail in half way.
You should try to Initialize phone to factory default system by Kies. You need seril number and device name. GT-9300 in this case. Kies will check Samsungs database and try to restore original firmware, also branded. Kies will try to repartition to stock layout, format and flash this firmware.
This option is somwhere in Kies menu, tools if I remember.
If its fail than only option left is try Odin, 3 files firmware, mx.pit and repartition check while flashing.
Wysyłane z mojego GT-I9100 za pomocą Tapatalk 2