It sounds like a mechanical problem. There might be a gall on the slide - the MaxNC uses aluminum-to-aluminum slides with just a thin layer of decorative anodizing between. Once that's gone, it's pretty easy to raise a spot that impedes smooth motion. There could also be a lubrication failure, or an issue with your plastic nuts, the gibs might need adjustment or the 1/4" leadscrew could be bent. Take note of where the error occurs and which axis is faulting, then disassemble the offending axis and check it out.
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