What do I do?  

RE: What do I do?

was it just using slot 4?  maybe the finda tripped.  I have had good luck with killing the power (I unplug the power cable), clearing the jam (I'm guessing filament is now lodged in the selector) then plug it back in.  there is the chance of it failing, but I would do that.  you might get away with hitting the reset button on the mmu, but I would kill the power myself in your situation.

RE: What do I do?

Yeah, just slot 4.  It was sliced in Slic3r PE, Single Material mode or whatever.

I think you're right, something tripped the PITA, PINA, FINDA, something sensor.  Filament, ah FINDA sensor.

I like your suggestion of power cycling the whole printer.

It would be great to get the selector back to slot 4.

RE: What do I do?

So much for that idea...  Forgot I was using octoprint to send the file.   So power cycle restarted printer, then octoprint started and restarted the printer again and sits idle.

Oh well.

RE: What do I do?

ahh damn, had I known the octoprint part...  but I have saved a few in my day. was there filament in the selector?

now.. you can move it to a slot when the power is off (just verify the hole matches up)  BUTT  when it turns back on I think it goes thru the selector calibration so it might move anyhow.

if it just screws up and no filament in the selector most of the time just hitting the reset on the mmu will work.

RE: What do I do?

Yeah, I realized it wasnt going to work right after I turned the power off.  ha.  Its ok... 

No, there was no filament loaded.  It unloaded before moving to slot 5.  Technically, it should have cycled to Slot 1 after it failed to load slot 5 so I am not sure... I am most certainly glad I did not have ABS loaded in slot 5 or PETG, that could have been ugly.

Reset the MMU or put filament in slot 5 but not really sure that would work either because when filament get loaded, it doesnt load all the way to the nozzle, there's a few mm feed that needs to happen and not sure that would have happened..  50/50  I guess.

RE: What do I do?

if all else fails move to track 1. you just need to push the selector. one lines up easy. 

if I am not mistaken. I  think the only things that can trigger selector movement with 1 filament would be is a sensor triggered a "filament out"

OR the mmu reset for some reason. this last set of firmware seems to trigger a reset every so often. but I think it seems to be at a Z change if the moon is in alignment with mars

ive had my share of "oh crap 13 hours in, and my mmu messed up, how can I save this"

in a way, saving a print is an artform.

RE: What do I do?

I restarted the print job and it did the same exact thing.  I played along, gave it some filament in slot 5.  It primed the nozzle just fine.  

Long story short I am pretty sure Slic3r had a brainfart on this file.  I closed/relauched and re-sliced and the gcode file is much larger now.

Third time is a charm they say..  

RE: What do I do?

I had this happen (more times than I would like).  Like you I was printing with octoprint. As a last ditch effort, I pushed the reset button on the MMU.  The MMU reset itself and started printing again.  I didn't even have to reload any of the filaments.

I think the communication from the MMU and the main unit is inconsistent at best.  I'm not saying this will work for everyone, but it did work for me several times.

RE: What do I do?

I think this is a MMU problem. No octo print here and I've had it lose its mind about the current tool.

I reset the MMU (little button next to the USB port) and was then able to get it to continue (for awhile before the next problem anyway...).

RE: What do I do?

Yeah - not Octoprint. 

I have 2 models that are of the same height.  Both had the first filament change happen at the SAME exact layer.   The first model, however, had several additional filament changes occur whereas the second only had 1 or 2.

I had a smaller model repeat the issue once but when I tried to reproduce the slicing, I was unable to and over-wrote the original gcode file. hehe

I am using Slic3r and .1 layers.  files are several MB in size.

Printed a model a couple days ago, 18 hours, only 1 filament change occurred thank goodness.

I noted the layers it occurred on at the time but looking at the gcode it notes height, not layers.   Not impossible to convert, just saying..