Which LW version are you using?
LW does install in various ways. It installs a receipt file inside the Library receipts folder. This could be copied across I guess. Receipts folder sample image. Not sure if it makes any difference it came from a different mac computer installation.

Are you still with Pro support & updates or has your Pro expired? Download another copy. Did you delete your previous installer? Why not just use that one?

Sounds to me like you are using LW 4, it's asking you to update to LW 5 right? You will do better with LW 4 I assure you.