According to LabView 7 Upgrade Notes >> Upgrade Issues >> Converting VIs, "When you open a VI last saved in LabVIEW 4.0 or later, LabVIEW 7.0 automatically converts and compiles the VI.". If you want to go backwards from LabView 7.0, the Save for Previous option only goes back to 6.1, but you can move to LabView 7.0 from 4.0 or higher.