You've lost connection to EA Servers Xbox 360

Disable Port Forwarding and DMZ (if any is set).

Enable uPnP.

Disable or allow the Xbox ports through the router's firewall (if it has one).

Setting up the router to have Static IPs for each Xbox's MAC is a useful thing to do even if it doesn't help the situtation. *Don't do this from the Xboxes, do it from the router via the Xbox's MAC

Power cycle the router and Xboxs, leave it unplugged for a few minutes.

Try it now.
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No?

All routers are so different in their firmwares... Try either checking or unchecking "NAT redirection" if you see it. Any type of security settings, try toggling them off if they are on.

Look for "Port Range TRIGGERING" use that instead of Forwarding.
Try using Port Range Triggering settings if uPnP refuses to work. (might even need to disable uPnP? *unlikely but weirder things have happened I guess. )

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I read somewhere that Xbox while in sleep mode (fast boot) doesn't request some of the needed ports to be opened when it's resumed.  That could be causing uPnP issues?

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Not all routers have settings like I descriped I doubt.  You may be able to load custom firmware on the router... but READ and REREAD the instructions before you attempt something like that.

Custom Firmware (like DDWRT or Tomato) would likely fix uPnP issues... making this whole thing a heck a lot easier.