[DragonByte Tech]

Does that one member have a vastly higher post / points generation than the rest of the member base?

If not, try adjusting the threshold setting you'll find directly under the target setting in vBulletin Options, then run re-calculate again (it won't change your points, just the targets).
I cannot tell you the correct setting for your forum, you need to figure that out by going to the leader boards and keep adjusting the number up (small increments) until you find a level that's appropriate for your forum.

Hope that helps