Couldn’t see sflow traffic sent from windows server 8(beta) box.

Hi, I was using wireshark 1.6.7&previous stable release trying to catch sflow data sent from my windows server 8(beta) to my windows 2008 R2 box. Using other 2 tools(netmon and sflowTrend) I could see sflow data sent to my monitoring box, but I couldn't see it in wireshark. Actually I could see it once but couldn't no longer and I didn't seem to make any change to the tool. I spent hours trying to change setting of the tool but still couldn't see any sflow traffic. Could anyone help me?