I'm also getting the Unable to charge battery with connected source, which is my laptop. With a USB wall adapter, 750 ma, I get the plug icon and lightening bolt on the RIM wall charger.
If I let it go to sleep it comes back on with the plug icon on the battery icon. I believe it is getting juice but letting you know that it is still in a discharge state.
Meaning, it will run longer but go dead eventually. 500ma supplied by the laptop USB is not enough to give it a positive charge. After it going to sleep and waking it the plug icon is still present.