It could be that your computer is occasionally busy doing other things.  

You might increase the network buffer size in Windows Media Player 10, which
might help.  Normally, the Windows Media Player handles this on its own, but
you can easily adjust it yourself, too.

Click on Tools >>> Options >>> and the Performance tab.  

In the middle of the tab, you will see a frame that reads "Network
Buffering."  Perhaps giving it a static 8 or 10 seconds of buffer time will
help.  The idea is to let the Media Player read ahead a little, like an
anti-skip CD player does.  Even if your disk drive gets busy, a few seconds
of music is still in memory and is unaffected by the drive's actions.  If
this does not help, you can always change it back to the default.