[dba-Tech] Win 7 Prof network puzzle

On this wired homebiz LAN (Netgear router), boxes A through F belong to 
one workgroup. A runs Ubuntu, B runs W2KPro with IIS 5, C and D run XP 
with Apache server 2.2, E runs XP Prof with no web server, and new box F 
runs Win 7 Prof with IIS 7.5.

-- all can ping one another

-- all can run web apps on A, B, C, D and F

-- B, C, D and E can access hard shared hard drives on one other

-- F can access shared drives on B, C, D and E.

-- *But neither B nor C nor D nor E can access a shared drive in F.* All 
those boxes report drive C in F is "not accessible".
Under "Ädvanced sharing " in F under Win 7 Pro, that drive is marked 
Shared, given a Share name, and given appropriate permissions.
And in the network and sharing center,
   ---- Network discovery is on,
   ---- File & printer sharing is on,
   ---- Public folder sharing is on,
   ---- Media streaming is on,
   ---- File sharing using 40|56 bit encryption is permitted,
   ---- Password protection is off,
   ---- Allow Windows to manage homegroup connecitons is on.

What am I missing?

PB