What other symptoms do you see immediately prior to/after the freeze?
I assume the music stops being played at end of song after media streamer freezes.
I first thought that it sounded like a network connection issue where Media streamer looses connection/control and locks up? (are you using DHCP, have you tried with manually allocated IP's for all devices?)
Then you mentioned file names and I have a vague memory of issues with some file types and naming strings?
PS, I have had similar problems when using Cidero (On PC) and Media Streamer on Nokia 770 to control playback and have not managed to pinpoint what causes the problem when it occurs.
On holiday at moment but will test when I am at home next week.