File download stopped

Scenario:
server: win2k, apache 2.2, mysql 5, php5, phpmydamin
pc: winxp, etc. etc.

Before:
from pc using phpmyadmin/win2k I was able to manage and backup mysql’s DBs to pc as dbname.sql

After
probably an AV update (maybe) is not more possible to backup a DB as it stay on download step always

All OK if I stop On Access protection on srv, (but this is not good of course).

Thanks in advance