Is it possible that they aren't in an assignment group for which that chat queue is configured?
You can have access to Agent Workspace and make your presence "available", but still not be in a group where you will be assigned work through a chat queue...and this is what will happen. It will say no one is available, even though someone appears to be available. They need to be available and in a group for which Advance Work Assignment has been configured to route chats to.
Look at awa_queue.list and find the queue definition in question and check out the "assignment eligibility" related list (tab) at the bottom -- make sure this person is in a group on that list.
Note that depending on the complexity of your organizations chat configuration(s), there may be other AWA configurations preventing assignment, even though they are listing their presence as "available" (skills, hours, etc)...
