The only way to open a VI from one version in the previous one, is to use Save With Options and select the previous version to save in. This way, however, you can only go back one version. So, if you have a LabVIEW 6.x VI, you will be able to save it with options for LabIVEW 5.x. Unfortunately, the oldest version of LabVIEW that had this Save With Options option was 5.1. So, the furthers you could go from LabVIEW 6.0 is to LabVIEW 5.0. You will not be able to open a LabVIEW 5.0 VI in LabVIEW 4.0.
Zvezdana S.
National Instruments