why I get a segmentation fault?

 hi, I now use xvid to decode raw mpeg4 stream from one PC on net, I use
a buffer to store the stream data, buffer size if 32k, when the length
of data in buffer >4k, I begin to decode from buffer. on the send side,
with KEY FRAME =1 , then one receive side,it can decode it with no
error! but with KEY FRAME = 25 on send side, in receive side, some times
it occurs "Oops: segmentation fault" while decode , why? which cause
this problem ?
any suggestion is appreciated! thanks!

and how can I use xvid to get realtime pic from one PC to other?

walker