Block the port 4500 or any 6500 first from being reserve for NAT overloading # ip nat settings interface-overload block port tcp 4500 or 6500 then you can use this port in any other command. 

You need to remove this port from the reserve ports for NAT overloading. Issue following command to block this port first# ip nat settings interface-overload block port tcp 5011 Then you can use this port else where.