I got below issue during a new 3+1 SQL server cluster environment setup for SQL Server 2008 R2 Enterprise. This is because you have already utilize this name as a cluster resource, as resolution you can delete this resource and proceed. Below is the description of the problem and solution.
The SQL Server failover cluster instance name 'SQLCluster01' already exists as a clustered resource. Specify a different failover cluster instance name.
1. Go to command prompt and run Cluster RES -- this will give you status of all the resources
2. Delete the orphaned user using the below command.
Cluster RES "
3. You are good to continue your installation now.