Here is a funny error. I have a dual extruder Axiom Airwolf that is hooked up to repetier host. Most prints work just fine, but occasionally. I'll come back after leaving it unattended and find that it's printing just fine...but not extruding. After checking the back to see if I have a jammed filament, I discover that the unloaded (unused) extruder stepper is turning and the other is disabled (but still hot).
The log indicates that a new tool has been selected but there is no tool change in the Gcode!
A brief google search has been fruitless. I think I'll re-configure the printer as having only one extruder as a temporary fix.