http://www.microsoft.com/mspress/books/sampchap/5726.asp
"Also, because TransmitFile is geared toward server applications, it is fully functional only on server versions of Windows. On home and professional versions, there may be only two outstanding TransmitFile (or TransmitPackets) calls at any given time. If there are more, then they are queued and not processed until the executing calls are finished."
It's not as official as MSDN I guess, but at least it's published by them. The article appears to be XP era.
Andrew
Yep, checkout MaxActiveTransmitFileCount here: http://www.microsoft.com/technet/treeview/default.asp?url=/technet/itsolutions/network/deploy/depovg/tcpip2k.asp
Can work around this particular fooness with EnableSendfile off. No idea if this will make teh problem disappear tho.
Bill
