There can be several reasons that may be causing this. Can you tell me more about your wireless setup?
The quickest fix may be to power cycle your modem and router (unplug and wait 1 minute, then replug).
I have got exactly the same message after we re-configured our router. I was connecting using my iMac wirelessly before hand, but now cannot. Our other PCs can connect wirelessly to the router so it's not the router. I have also tried the firewall solution but that doesn't work either.
I did call Apple Support who said that a full troubleshoot would cost £35 as my computer is older than 90 days (well yes it's been working fine that's why it's over 90 days old, it's only now that it isn't!). He said a trouble shoot didn't guarantee success so I declined his offer to charge me an extortionate amount of money for nothing! He did say that the router needs to be giving the Airport an IP address, but it isn't doing it now. His only suggestion was to turn off the router and turn it back on or power down the iMac. Neither of which help.
Anyone else had any success?
I've had the self-assigned IP address problem with my university's wireless network for several months, and I've searched and entered help tickets and no joy. However, I searched one more time before giving up and found some suggestions in another Apple discussion thread
The one that worked for me was to delete the Airport item from the list of services in the Network System Preferences window, then add it back again. Apparently, this reconfigures the Airport settings and makes everything all better.
Hope this helps!
System Preferences > Network > Airport/Wireless
Use the gear below the list of Interfaces to choose "Set Service Order" and put Airport/Wireless at the TOP. This will make a big difference.
Click ( Advanced )
In the Wireless/Airport pane, be sure the Networks you most want to join are listed at the top of the list, and feel free to delete any you don't care to join automatically. Once you have a good list, check [√] Ask to join networks (rather than just joining them).
In the TCP/IP pane, set IPv4 to DHCP and set IPv6 to OFF.
Addresses from the "self-assigned" range (169.254.xxx.yyy) appear for everybody who uses DHCP to get an IP Address. Most users never see them because they are so quickly replaced by a good IP address and they go about their business.
When you are stuck with a self-assigned address, it means the Router will not talk to you to give you a better IP Address. You should suspect primitive things like bad cables and massively messed up configurations.
You can fix most configuartion problems to get things going by using:
System preferences > Network > Ethernet OR Wifi/Airport > ( Assist Me ) > ( Assistant... ) to set it up again from scratch by answering the Questions.
I had the same problem and this solution from Apple support worked for me (using Airport):
In Applications Open Airport Utility
Click on Time Capsule Picture then Edit
Click on Network
Check Router Mode is set to: DHCP and NAT
Click update at the bottom
If red error symbol after update:
Check Status if orange light and says Double Nat, click on Double Nat and then on Ignore