Cisco 2821 & Cisco 1841 Connection Trouble

Hello All,
looking for some assistance if possable, i am involved in setting up a brand new network in our workplace. We have a Co-Location site in Melb CBD which has a Cisco 2821 running. Office #1 has a 1841 router connected. From the 2821 we can get to the internet and back into the IPMAN/IPWAN no problems. From 1841 i can ping everywhere in IPMAN/IPWAN and to the IPMAN side of the 2821 but not past this router to the outside world. What am i missing?