Airport Express Manual IP address problem

[ifjake]

I tried this at apple.com and haven't got a response, so I'll try here. Right now I'm connected via Ethernet to a local network. The tech guy here has us all hooked up with manually assigned IP addresses that we type in ourselves. I would like to hook up my Airport Express to the network instead and have that be my personal private wireless hookup, but when I try to configure the Airport Express with the exact same numbers, I get an error message along the lines of: "IP address, subnet mask and router do not match up. Cannot update base station. Please fix." The odd thing is that I have exactly the same numbers for each the IP address, Subnet Mask, Router number, and DNS Servers I have right now in the Ethernet Network preferences of the laptop I am right now using with these settings to connect and send this little post out. So why does the Airport Admin Utility for my Airport Express not allow these numbers to go through when manually inputted, while the System preferences of the laptop does?