Hi -- The error is coming from the On_Cue_On_step which I assume is a telescope mount control system? I can think of a couple of reasons but I am guessing:

1. The alt/az for the light panel is outside the range of permitted altitude for slews
2. The mount cannot do Alt/Az slews but is reporting to ACP (through its ASCOM interface that it can do them). ACP believes this and will call SlewToAltAz. If the scope reports that it cannot SlewToAltAz, then ACP will call back to multiple RA/Dec slews to get to that altz the hard way.