Sergio,
Also note If your source 7-mode volume contains iSCSI or FCP luns, these cannot be transitioned to a Clustered Data Ontap SAN. You will see this error in the SAN log:
wafl.voltrans.lun.exists: Volume <Vol-Name> contains 7-Mode LUNs. It cannot be transitioned to Cluster-Mode.
You must manually copy the data or use an imaging software such as Shadow Protect or Symantec Backup and Imaging Software for example.