What year machine? If it has mechanical switches the one that detects the OUT position may be hanging up occasionally. I think this would give an alarm because the control applies power to the shuttle drive motor and looks for this switch to open. If it does not open then the control alarms because it thinks the shuttle is jammed.
If it is a newer machine with proximity detectors there may just be a chip near the detector.
For mechanical switches that are gummed up with dried coolant I spray them with methanol (methyl hydrate) or isopropanol (rubbing alcohol); this dissolves most coolant residue. For proximity detectors just wipe any chips off.