Happens to me too. It can happen when restarting it too quick I guess because it takes a couple secs for it to fully close the old instance. I guess the faster your computer the less it would happen. For example same thing happens to me with sys-firewall if I start it too quick after the sys-net, basically before the sys-net has internet connection, which will cause an error as well.
To avoid this now, instaed of manually starting the sysnet or proxies, i just load the appvm i want to use. So this way the sys-net and sys-firewall and proxy is automatically started at the proper intervals one after the other avoiding me accidentally starting one of them too quick. But you still have to give it acouple secs after first closing the sys-net .