1. Sometimes Grooveshark updates how they do things, this may cause GrooveWalrus to stop working. You can try using the Flash plug-in, while you wait for a fix to be posted on this website.
2. Grooveshark sometimes doesn't work for awhile, check their website and see if you can play a song there. You can wait till you can play music on grooveshark.com OR try and play a different song.