It can happen that the chargers, as they make their full charge move straight after the intended target (or right through them!), run into another enemy unit that is in the way of their move. Note that this may happen even if the original target is now so far away that the charge has failed.
If the charging unit would run into another enemy, they are allowed to immediately declare a new charge against the enemy unit now in their way.
The chargers do not have to do this, and can instead choose to stop their move 1" away from the enemy, as normal.
If the chargers decide not to stop their move, the player must now declare that his unit is charging against the new target, and the target must make a charge reaction as normal. If this second target flees as well, so that another unit lies in the way of the new move of the chargers, this procedure is repeated until the situation comes to either a successful charge or a failed charge.
The following is an expanded explanation from the Official 7th Edition FAQ from December, 2006.
Situations may arise where a unit can charge the same target mulitple times because of the Enemy in the Way rule. An enemy may declare a flee reaction, which takes it out of the position of being charged by a unit, such as behind another enemy unit. If that second enemy unit, which is in the path of the charging unit, also flees, it is possible for the chargers to declare another charge if they are not in the path of the second charge.
**For example, the initial target (unit A) flees through friendly unit B (which doesn't panic), stopping just behind it. The charger may thus change the charge towards target unit B. Unit B then flees as well, going through unit A. The charger may once again change the charge towards unit A.
Note that units that are charged again through this process do not get a new charge reaction, which may sometimes mean that when the charging unit will finally move its full charge distance, it may destroy several units that fled from its charge (see diagrams below).