It is might be possibility that your VPN client and your firewall protection incompatibility.
You can use “tracert” to find out which node is causing the problem and send report to you ISP end.
tracert may not give you the best picture. A better tool included in Windows XP is pathping.
pathping is an excellent troubleshooting utility to look at latency & packet loss along a path.
Usage: pathping [-g host-list] [-h maximum_hops] [-i address] [-n]
[-p period] [-q num_queries] [-w timeout] [-P] [-R] [-T]
[-4] [-6] target_name
-g host-list Loose source route along host-list.
-h maximum_hops Maximum number of hops to search for target.
-i address Use the specified source address.
-n Do not resolve addresses to hostnames.
-p period Wait period milliseconds between pings.
-q num_queries Number of queries per hop.
-w timeout Wait timeout milliseconds for each reply.
-P Test for RSVP PATH connectivity.
-R Test if each hop is RSVP aware.
-T Test connectivity to each hop with Layer-2 priority tags.
-4 Force using IPv4.
-6 Force using IPv6.
It’s not a gui but it does give very valuable information within a single utility about the path between a source & destination.
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