The CR Unit cannot track the Home position to set the CR origin. False origin detection due to paper jam or the like. Misreading of CR Scale. CR Lock is damaged.
Check if the paper is jammed. Check if the CR Scale is read out properly. Check if the CR Scale is damaged or contaminated. Check if the CR Lock functions normally. Re-install the CR Encoder. Clean the CR Scale with ethanol. Replace the CR Scale. Replace the IS Unit.