It will play about a minute and a half of a song and freeze up. Sometimes for a few seconds, sometimes for more. The files I am playing are standard MP3s. Not sure what the issue is. Does it need the USB stick to be in a specific format, i.e. fat32, etc?
I had that problem on my 550i a few years back, try getting a faster flash drive. I got some Kingston Traveler model that had faster read/write speeds than most flash drives on the market back then and I've had 0 issues with it ever since.