MMU2S PREHEAT ERROR - solved
When printing filaments of different materials that require different temperatures, the print would stop and the PRUSA display would display PREHEAT ERROR.
There appear to be two causes.
First, there appears to be a bug in the current Slic3r PE that doesn't take account of the proper temperature changes when printing with different materials at the same time. nikolai.r created a post processor that will read the Slic3r PE file and automatically fix the temperatures, writing a new GCode file that can be used. Hopefully the Slic3r team will fix the bug soon, but until then you can find more info in this thread:
Second, if the fan is always running at 100%, it can be hard for the hot end to heat up quickly enough - triggering the error. Filament Settings > Cooling > Keep fan always on = unchecked did the trick for me. I left Enable auto cooling = checked. Be sure to do this for all of the filaments that you are using in the print.
Hope that this helps others.
- Brad