After changing the client revision, the program still does not work anymore. The response when searching for a song is "Bad Token". After taking a look with Tamper Data it seems that the communication token is not used "as is" anymore when sending a request to Grooveshark, but is now longer and different for every request.
The new token probably hashes one or more of the following: time, the communication token, the song title, other, but it's pretty hard to figure out how it is formed exactly. Do you have any idea?