I got here via a Google Search because I was having the same problem. I was also thrown off by the default switch to a gzipped version of the gcode file, but swapping to uncompressed gcode didn't help. I did open the file to look for problems in a text editor, but found nothing amiss. Our error pointed to line 13, which just specifies the buildplate type. All that said, we updated the firmware on our UM3 and that resolved the problem.