I encountered an error the other day when downloading Windows Embedded Compact 7 to a Windows Virtual PC on a Windows 7 host machine. Platform Builder initially started the download process and then immediately stopped with a TFTP time out error.
I found this entry on Olivier Bloch MSDN Blog:
http://blogs.msdn.com/b/obloch/archive/2010/08/12/windows-embedded-compact-7-and-virtual-pc-bsp.aspx
It seems that disabling the UDP check sum for IPv4 on the Ethernet adaptor shared between the host Windows 7 computer and Virtual PC solves the problem:
