On Feb. 25, Houston Mayor Bill White announced to much fanfare that ChevronTexaco had agreed to buy the former Enron building in downtown Houston. But this Chronicle story today indicates that the deal apparently has developed an unexpected hiccup: Mayor White’s eagerness to make the announcement of the deal may have undermined ChevronTexaco’s ability to receive millions in ad valorem property tax breaks from Harris County that it assumed that it would receive in deciding to buy office building. Ooops!