We've been struggling with the same issues we're an MCP so we raised a ticket as MS....

Its been raised on this forum before

http://www.sqlservercentral.com/Forums/Topic339239-291-1.aspx#bm339851

Thank you for contacting Microsoft...

have you got a broadcom network card in the server? is it running win server 2003 sp2 ?

if so try turning tcp chimney (via command line) and synattackprotect (in registry)...