1st gen Apple TV loses 5 GHz network

My 1st gen Apple TV stopped seeing my 5GHz 11n network today. The network is provided by a 2nd gen AEBS in 5 GHz N-only mode (I have a separate 2.4 GHz wifi router). Everything was fine this morning (played music using the iPad as remote). During the day the status LED turned solid amber (which I think is an undocumented state) and the Apple TV was off the network. It did continue to work as normal though. It can also see (and connect to) the 2.4 GHz network.

I've had this once before, a couple of months ago. I did a factory reset then which solved the problem. I did that again today, which looked promising initially, as it did see the 5 Ghz network again, but after re-upgrading to 3.0.2 it lost the network again.

The 5 GHz network is used only be the Apple TV, two iPads and a MacBook. All three didn't experience any problems with the AEBS. There are no other 5 GHz networks in the area. As both AEBS and AppleTV are "old", none had any firmware updates in ages.

So my questions are: what does a solid amber LED mean? and what could cause the AppleTV to not see the network it has been connected to for ages (at least 3 years trouble free).

Louis