3181 X axis programmed into endstop.
This error indicates that the X axis has been programmed beyond the axis travel limits, perhaps an incorrect +ve or -ve direction sign or offset. Cancel the error and correct the programme.
If the 3181 error persists the fault may be with the 'Watchdog' board (WD 50x) in the control or corruption of the memory. If another control is available the 'Watchdog' boards can be exchanged to test. If the memory is to be reloaded remember to punch-out programme and tool information first (although an up to date back-up tape should always be held).