Printer system error Layer 51

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Hi,
I have had this happen several times now on different prints, but it doesn`t happen every time.
The printer will suddenly stop, all I have to go on is the message in the bottom right of the screen saying 'Printer system error Layer 51'
I`m not sure if the number is always 51 but it was just a few minutes ago.
The only way I know to get out of the situation is to press the initialize switch, lowering the bed and aborting the print.
Has anyone had this or know the cause?
Thanks