2nd Extruder stops mid printing

Hello,

after some hours of printing (around 15h) without problems I tried my first 2 colour print. But mid printing the second extruder stops extruding, but it extrudes without problem when I manually control it with the display, after it stops extruding.

After this happened I tried the same G-Code again, but it happens again. Just this time it confused extruder 2 with 1 and printed the brim with extruder 2 instead of extruder 1 (=wrong colour and it was moved to the left side), the rest of the print was printed in the middle, but it stopped again like the first time.

I already did the XY-Carriage Alignment and could print on extruder 1 without problems. And I don’t think it is the 2nd extruder, because it extrudes without problems after it stops extruding in the print.
I have heatsinks on the stepper drivers and print directly from sd card.

My Filament:
Extruder 1: original Velleman PLA, black
Extruder 2: filamentworld.de PLA, white (data sheet: filamentworld.de/wp-content … ET_PLA.pdf)
Temperatur: 210° (standard setting, booth extruders)

Anyone has an idea what’s wrong with my printer (if anything, than what’s maybe wrong with my settings in Repetier host (Vertex Edition))?

Thank you,
[size=50]and sorry for my english.[/size]