This happens pretty regularly for me on OSX, and has been happening since at least Android 1.5 I think. There are a few google hits on this, but not much, and this is likely in part that the error message can't be copied and pasted, and most experienced coders simply click "OK" and move on, but it's very confusing for newbies.
You'd have thought that a big company like Google could get this fixed up. Maybe no one cares enough - maybe it's only happening for a few of us. Maybe I'd have to bring it up at Google I/O or something to get it fixed.
In general though any other kind of error that can be copied and pasted is usually easily solved via StackOverflow, e.g. when the ADT tells me that I can't install an app due to an existing one with the same signature and I have to type "adb uninstall whatever" in a shell and then I get this from the shell:
unknownc8bcc8da38b2:platform-tools samueljoseph$ ./adb uninstall edu.hpu.csci4702
- waiting for device -
error: more than one device and emulator
So I google the error message in quotes and I go to the stackoverflow hit since that's usually the best way to make progress:
and I see how to uninstall from a particular device. So that all kinds of work, but I wonder why these IDEs couldn't be a little more user-friendly - I have similar issues with XCode. With both XCode and Eclipse ADT I feel like a lot of disparate tools have been bundled together and are not quite working properly. Maybe that's just the nature of things ...