The message gives the mac address of the duplicate. on a small network the brute force method of get all the mac address of all devices and figure out how it got the address. In most cases there is a problem with the DHCP....most likely you have multiple device giving out addresses. Check the ipconfig /all and see the address of the dhcp server and even check the arp table to be sure even if it has the same ip it has the same mac.

The speedstream is actually a router so you could have DHCP enabled on both routers.