Time to check that firmware. As reported by ExtremeTech »www.extremetech.com/article2/0,3···8,00.asp a faulty ddns client implementation on the WRT54G has flooded Worcester MA DDNS' servers to the point that they have taken action. Unless you have the fixed firmware (characterized by DDNS as "good enough" while still containing glitches), you will be blocked from using the DDNS service.
DrTCP Yours truly Premium,ExMod 1999-04 join:1999-11-09 Round Rock, TX
Link from DynDns.org
After Netgear routers DoS'ed Time Servers, LinkSys DoS attack popular DynDns.org. DynDns.org is now blocking WRT54G routers unless you have code having fix.