try ipconfig/renew
that should drop your current IP address and ask the router for a new one;
which hopefully will be different.
If that fails (or you'll get a new IP address and still have the same error),
you're likely runnning a virtual machine of some sort, that shares the IP address;
you need to reconfig that VM or allow windows to share it's IP with said machine.
'sid
[
EDIT]
Sorry.. that's the quick and dirty xp way

for newer wíndows, run cmd as administrator, and in case "renew" doesn't do;
first release

ipconfig /release
ipconfig /renew
that'll work for vista, 7 and 8 (don't know about 10... but I guess it'll still do)