I constantly run multiple instances of Ping Plotter here, and I've not seen this on any of my test systems (Test OSs: 95, 98, ME, NT, 2000). Of course, this doesn't mean that it's not happening.<br><br>Ping Plotter uses the standard Windows ICMP.DLL method of creating echo requests (Pinging). This method appears to be very thread-safe and resilient to multiple oustanding requests on the PC level.<br><br>If you're running from the same PC and same setup of Ping Plotter, then this probably isn't the reason, but you might check to make sure you're using the same packet size on both instances. Different packet sizes and different contents of packets can cause varying results from the same router.<br><br>Some routers don't respond well to multiple outstanding ICMP echo requests. This is something I'm seeing more than I like lately. It's possible that your router does OK with a few outstanding requests, but when you get two instances at the same time, this overloads the number that it handles well. If the culprit is your router, the problem can sometimes be fixed by updating the bios for the router (this was the case on my Cisco 675).<br><br>Is the packet loss showing up right on hop 1, or is it hop 2? Does this happen reliably (ie: adding a second instance of Ping Plotter causes more packet loss to appear)? If you post (or e-mail me) some of your results, I'll see if the details give some additional information about where the problem may be originating.<br><br><br>