Oxford ebike problem ?

Hello, i have recently problem with my oxford ebike it's made in 2010 I think but I bought it last yeay and was working very well but before few days ago I started to have problem when I ride it suddenly the speed goes down and the motor stop working but if I off the display and wait for 3 min or more and press the button of the display again the motor works again but it didn't work always when I off the display but it shows in the display error 6 I don't know what it means can anyone know why I'm facing this issue?  The display is Tranz X Pst. Thanks