I have a windows 2003 server that not each 30 minutes aprox lost connection
with the rest of network, I changed the server and the problem continues,
because of that I think that de issue is some workstation, I saw that
restarting browser explorer service the connection was restored however few
minutes ago the problem came back

The workstation has windows XP SP3 AV symantec 10.2 and nod32.

any idea is welcome
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thanks
PL