Variable Sets created with earlier versions of the software are always compatible with new versions. You can import them and use any new features of the software as required. No error messages will be shown.
Variable Sets created with newer versions of the software than the one you're using can be used as long as no new settings were used (as they are not supported by the software). If there is a version mismatch, one of the above mentioned error messages appears.
If you can import the Variable Set, remove or change the variables containing settings that are not supported.
If you cannot import the new Variable Set, you can either upgrade the software (recommended) or re-create the Variable Set using the older version of the software.
Note that, while saving Variable Sets, Enfocus PitStop Pro will automatically choose the lowest possible Variable Set version number to ensure maximum portability.