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.
I have a Speedstream 5100 modem running AT&T DSL. I've set it up to run through a Netgear Rangemax router (both the devices are fairly old, 2005 or so vintage.) The router worked fine connecting multiple devices before, but a different connection through a different modem. Now, however, it will not connect more than one computer at a time. Whenever more than one computer tries to connect to the router, the other people lose internet access and Windows 7 says there is an IP conflict.
I'm not sure how to get rid of this IP conflict. when we tried Run>cmd>ipconfig/renew, we got an error message saying No operation can be performed on Wireless Network 2 while it has its media disconnected.