Problem(s) Encountered:

The MaximDL guider was set to a 128 box.  At one point, it totally lost it and started guiding as fast as it could in one direction, consistently.  This was apparently caused by a hot pixel near the edge of the guider box, which the telescope was trying to follow.

Solutions:

Switched to a 64 pixel box, and had no further trouble.

I''ve seen the guider get pulled off transiently by a cosmic ray hit in the track box.  For this reason, if forced to use a faint guide star, it is better to increase the guide time so there is less of a chance that a cosmic ray wins. [Halpern]