"invalid gcode" is an firmware issue.
"cannot cold extrude" is probably caused by weird firmware. It could be caused by Cura as some times of printer don't want a set temperature g-code before they start printing. Try selecting different printer types (UMO should work) to see if that helps.
' i think we all know the quality of the micro M3D printer '
You do know you are on an Ultimaker forum, don't you?
What printer profile do you use when dumping out a gcode?
You need an optimized profile for your specific printer otherwise your bound to run into problems.
Without having seen your prints (don't know if you are dealing with a software or hardware), I think part of the problem is buying one of the cheapest 3D printer around.
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