I had the same problem trying to charge my m11 thru the charge cord on my much more cell master last night set at 2500mah cap. and 2.5 amp charge, i think the voltage needed to try to charge the cells at that high of a setting requires more voltage than my power supply was able to put out, so i used the same charge cord and hooked it up to my hobbico quick field charger mkII pro series that i use for my lipo in my 18r and my gliders, set it to its max amp setting and set it to nimh and had no problems at all, i did stop the charge a little early because the cells were getting a little warm.
If i were you i would try turning down the amperage between 1-2 amps and see if that helps.