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Was the Mackie loudspeaker in question working, before this problem happened? or is it a newly installed loudspeaker that has never worked before?
The "Voltage!" warning means that your loudspeaker has sensed a problem, which is either with the voltage applied to it, or more likely a problem with the internal voltage.
Is this Mackie loudspeaker system older than one year from purchase date?
Check the outlet it is plugged in to, by using another device plugged into that outlet at least briefly.
And check the cord leading to the speakers that supplies the power. Make sure there is no breakage nor strain in those cords.