it means that you have a running server on the same host and on the same port. It could be caused by a previous execution who never shut down the server. You could try connecting to the server and shut it down, if you have a client, or verify if there's a server running. Since you are on CentOS you could understnd with a :
ps faux | grep Rserve
If you see a row like
root 23762 0.0 0.7 211304 28632 ? Ss 14:11 0:00 /usr/lib64/R/bin/Rserve
then you know you have it. You could kill the server and re-run your tool.