So, just had a couple of people in the store with the same issue on the Fascinate where they were getting a "Download Unsuccesful" message on any attempted app instals in the marketplace. The steps I took that solved the problem are as follows: Be sure the phone is signed in to Google Talk. Go into menu-->Settings-->Applications-->Manage Applications Locate, open, and "clear data" for Google Apps, Google Voice Service, Download Manager. and Google Talk Service. I didn't do any resets or anything after that; it just started working. Hope that helps.