Problem(s) Encountered:

Trouble due mainly to operator error: platform was left slightly raised after an instrument tweak and in the middle of the night the telescope stopped guiding and tracking during an observation. 
Telescope was sent to zenith to diagnose and during this slew the instrument rotator rotated (locking screw freed) presumably due to contact with railing.  The rotator was not powered, so we couldn't reset the rotation angle to 0 (and also wouldn't have been able to re-lock rotation). Because of this, we left the instrument in this position for the rest of the night.

As far as we can tell, instrument and telescope systems are working. We used the time to install, focus and test the high-resolution microlens array. We obtained lamp and some non tracking sky calibration data towards the end of the night.

Solution:

Retaining pin to limit rotator motion bent.  Tony cut it out, cleaned up the threads in the rotator plate and fabricated a new pin.  All telescope/instrument operations checked out OK.It may be recalled that the telescope used to have an interlock that killed power to drives if the platform was moved out or up.  That interlock was bypassed during the 2017 TCS upgrade.  I will look into establishing an interlock for the future.