Same way you troubleshoot anything. Start removing things
till it works better. Do you have problems if the Client is
on the LAN with the server? Try running a player ON the sever.
Aside from that things to consider: Does it matter how many
clients you have connected (ie it's fine with 1 but bad
with 100)? Are the right ports open on the firewall to
allow RTSP and MMS connections to get through? What about
network latency what do client to server pings look like
over a day or so? Network usage low? General rule of thumb
is keep it <70% and you'll be ok.

Hope this helps.