Sometimes a charging unit can move into contact with its target, but cannot close the door because something else lies in the way, normally another unit or a piece of terrain. Where this happens, the charging player should attempt to complete the charge in such a manner as to avoid the obstruction. This can normally be achieved by increasing or decreasing the amount the charging unit wheels as it moves, or changing how the charging unit closes the door. In some cases the enemy unit might have to close the door with the chargers instead. If no amount of finagling can allow the unit to avoid the obstacle, the charge fails.
There is one important principle that you should always keep in mind when charging: under no circumstances can a unit use its charge move to move into contact with an enemy it has not declared a charge against.