Cyclocephala sp. (Masked Chafer).
Size: approx. 10 mm. Photo: 09/10/11, 11 pm.

This beetle is a Masked Chafer (Cyclocephala sp.) walking on my window screen. The genus has 21 species in North America. Adults are attracted to lights. Larvae (white grubs) are root feeders and many species are considered agricultural pests. 

bug guide (these photos):