I solved the issue with an intensive search and I found the following:
Since Windows Vista MS optimizes the TCP throughput, especially for
transmission paths with a high BDP, the Next Generation TCP/IP stack supports
Receive Window Auto-Tuning and some network are not ready to such changes.
So, recently we changed the core network switch in order to scale our
bandwith to 10 gigabits. We are in contact with our hardware supplier in
order to assure us that the new device supports the "Receive Window
Auto-tuning" parameter. In the meantime we disabled the parameter in the
servers with networking issues and now the servers are working fine. The
command to perform that task is: NETSH--->INTERFACE---->TCP---> SET GLOBAL
The only thing that is oddy is why the server with windows 2008 Ent 32 bits
is working well when it has enable such parameter? Is there some networking
guy that can explain that for the community benefit?
Thanks a lot to MS and its contributors for the excellent links!!!