A bit of a necropost, but this is one of the top results for this error and I think it would be helpful to have some more information here.
I'm running echoprint on Ubuntu 12.10, and successfully started the server, ingested a song, and made a query. Then I stopped the servers and restarted my computer. After starting the servers and making a query, I got this unusable response error, before and after re-ingesting the track.
I expect this is because ttyant is configured to store data in-memory as pointed out here:
http://developer.echonest.com/forums/thread/713 which I think is default for the ubuntu ttyrant package, and thus restarting wiped my ttyrant database, but not my Solr database, so they are out of sync.
I haven't got it working again, but I think I will try wiping both databases and seeing if that fixes it. Then I'll see if I can get ttyant to keep its data.