Problem(s) Encountered:

...the guide probe is stuck in X.  I do need to guide, unlike Doug, so I tried to fix it, going as far as re-initializing the MIS, but it won't budge.  

I was able to establish with some confidence from the guide star fields that even though the MIS claims the probe is stuck at X = 0, it is out near X = 23000.  

Solution:

x-stage home limit switch failed.  It essentially disintegrated.  Replaced the limit switch and tested systems. Should be good to go.