AVG 8.0 Free on XP blocking internet

Have AVG 8.0 Free on two XP computers. Both had internet blocked that seemed to be occurring after AVG either updated, or attempted to update. Both Firefox and IE were blocked. Have deleted AVG 8.0 from one computer and problem solved (installed another anti-virus program in its place). Other AVG 8.0 computer still has same problem, but I notice that if I leave it on for a couple of hours, problem resolves itself and internet access is restored. Can anyone help me.