Aloha everyone,
I get that same error message on my 15" MacBook Pro sometimes, although I don't get it on my 20" iMac. For some reason, the iMac gets a better signal than my MBP - maybe it's a better NIC. It doesn't really bother me that much. I mean, sometimes recycling the Airport works, but I also have a network cable in my computer room anyway. When I go to my bedroom, I get a consistently good signal on my MBP - the problem is only in the computer room, which is the farthest from my AP (it's in my brother-in-law's room, as the cable access is really for him - I'm just leeching off of him).
One other issue was one of my own doing. If your router is also a DHCP server, make sure that your IP pool is large enough. I use DHCP until the computers on my network are assigned an IP address, then "clone" the assignment (D-Link's terminology) to a static assignment within the router. In other words, only the computer with the MAC address matching that particular assignment will be assigned the corresponding IP address. I had limited the pool to the computers in my house, then I bought my MBP. I couldn't get on the 'net with the wireless NIC until I opened up the pool for one more assignment. In other words, it went from 192.168.0.100 through 192.168.0.105 - I needed to let it go to 192.168.0.106 so that my MBP could get on the 'net wirelessly. Once I opened up the pool, I was able to get on with no problem. Still, I'm pushing it a bit with the range and obstacles - it's 902.11g, but I have a few walls/corners between my AP and my computer room.
HawaiiMacAddict