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Using Rostock Max V2, MatterControl 1.6.1. I posted about this on 9 January but the problem went away until today. It is only happening with one set of four parts printed as one job. See the photo.

The hot end descends toward the bed and sort of goes crazy before it reaches the bed. There is a video of this behavior at this link. https://drive.google.com/open?id=0B83XK ... jhjOG1vWm8

I have printed this particular job numerous times since the tenth of January and had no problem. Today, I have printed the job twice but in between these two good prints, I have had to turn power off to the printer and start again five times.

Does anyone have any suggestions as to what might be causing this?

If I were just going by the video, I'd say there's a problem with homing the printer... it looks like one of the towers is off when it homes and that's coming out in the position error... but that doesn't match your description of the problem. Still, can you get a video of what it looks like when it homes at the start of the print up until it start air printing?