If you want to add a node to cluster and the procedure is stopped with message “Cluster node already exist” means the node is registered on Active Directory. This message appear after a restore of operating system or in some trouble cluster installation. The situation can be unlocked with a special command line.

BE CAREFUL the following command are irreversible

Open a DOS shell (Start -> run -> cmd)
put a command “cluster node/forcecleanup”
must appear a messagge “clean up successfully completed”
re-run the operation for adding a node to cluster