If the charger will not commence the charge then the pack has more than likely dropped below min voltage (C x 3.0v)
Ive never heard of a charger not starting the charge because the cells are way out of balance
Chances are they are damaging their packs if they are taking them this low
Better advice would be to get them to not run as long or set their LVC's higher
Assuming they set their LVC's for 3.4v or so they should be aiming for a resting voltage of 3.7v / cell
Cheers