This is the most common error suffered with Age of Empires III multiplayer.
This error can be caused by many problems, and consequently, there are many methods to try to repair it.
After each numbered step, attempt connecting to several games in multiplayer; only proceed to the next if you are still experiencing issues.
1. Allow Ensemble Studios Online more time to load.
(This solution needs done every time you log in -- you might further try more steps if you wish to not have to wait every time.)
2. Try power cycling your network hardware.
3. Ensure Age of Empires III and its expansions (age3.exe, age3x.exe, age3y.exe) are listed on your firewall's exception lists; try playing with the firewall in Gaming Mode, Low, and Off.
4. If you connect to the internet wirelessly, try a wired connection.
5. Toggle UPnP on or off.
6. Try Port Forwarding UDP and TCP ports 80, 2300-2310 to your device.
7. Try Port Forwarding UDP and TCP 80, 2300-2340 to your device. Note the larger range of ports than step #6.
8. Override the Port to 2300.
Use the parameter OverridePort="2300"
9. Override the game to use the correct IP address.
Use the OverrideAddress= parameter with your IP address.
10. Try setting the DMZ on your router on.
An error that usually occurs on Windows 7.
After each numbered step, attempt running the game; only proceed to the next if you are still experiencing issues.
1. Ensure the game is Running as Administrator.
2. Try running the game in compatibility mode.
For this issue, see instructions here.
Problems with ESO Accounts should be first solved with the Account Management Tool on the official site.
If you have further problems that cannot be solved with that tool, create a Support Ticket. Be sure to include your Product ID.