Receive error when try to connect POX using custom topolgy in mininet

[BabakMemar]

I have created a custom topology as following and run it using mininet and connect to POX remote controller.

class CustomTopo (Topo):   
    def build(self):
        S1 = self.addSwitch('s1')
        H1 = self.addHost('h1')
        H2 = self.addHost('h2')
        self.addLink(S1, H1)
        self.addLink(S1, H2)

topo = CustomTopo()
net = Mininet(topo)
net.start()
topos = {'mytopo': CustomTopo}

It worked correctly first time, but after that I received following error in POX controller when it tried to add links:

Caught exception. Cleaning up... Exception: Error creating interface pair (s1-eth1,h1-eth0): RTNETLINK answers: File exists

What can I do to solve it?

[MurphyMc]

That doesn't look like a POX error. Maybe that's a Mininet error?

[BabakMemar]

Thank you dear Murphy You are right, it seems that this problem relates to mininet.