he was denied admittance to the very formal party for not be

dressed 过去分词做形容词用（还有：talented,gifted,etc）,穿戴好的 有。穿戴的 be dressed properly 穿戴得体for 介词 后跟名词,需用动名词形式,for not being dressed properly 因不得体着装其他回答也有道理（然似被动因素不强）,权作参考,敬请修正。