[Brian R.]

The top bolt cannot be removed. The pump is held by that bolt through a slot in the pump housing. The pump is removed by loosening the top bolt, then the bottom bolt is removed. Then the pump slides from under the top bolt. You need to loosen the upper bolt to remove the other bolt. You may need to remove the fender aprons seal for access and/or use an open end wrench.

(You may possibly be trying to remove the wrong fastener. There is another nut that is behind the pulley and much more difficult to access. It is not necessary to loosen this nut to remove the pump).