You'd be better off using our import page in your LimeLM dashboard. Just export your old data in a CSV file and you can then import the product keys using our new importer form. There's a link to it in the version you want to import the keys to:
[attachment=0]version-sidebar.2.png[/attachment]
Just click the "Import product keys" link and follow the instructions (choosing the fields you ant to import to, etc.).