Crashing the operating system into the Korg PA700

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I'm having some wierd issues with Korg PA700 keyboard.
My setup:
It is connected to Yamaha MD-BT01 with the iPad and it works with SongBook. The MIDI setup is 07 Tablet. Everything is correctly parallel programmed. The link works with the use of codes (3 and 4 digit). There are no duplicate codes. It worked perfectly for 2 months but then crashed 7 times in a row. There was noise and I couldn't shut it down with the master volume. Rebooting it, was the only solution. The error usually repeated itself after 5 minutes or so. I have reinstalled the operating sistem, and it's working fine for about 5-6 hours now. Does anyone have an explanation? Did anyone have the same issues?