Sassy72 –
OK, you’ve confirmed that the driveway is Common Property (which I must say sounds strange given your description of the layout), and your next task should be to ascertain if what the tenant told you is true; assuming of course that you want him to stop parking on the driveway.
If that’s the outcome that you want, then your Strata Manager should know who the tenant’s Property Manager (Rental Agent) is from the Notification received under S119 of the Strata Schemes Management Act (in NSW), so ask him/her to contact that person and find out if the driveway is included on the Lease. You should also keep your Executive Committee Secretary in the loop.
That said, whether the use of the driveway is or is not on the Lease, your Strata Manager needs to advise the Property Manager that their tenant is parking on Common Property in Breach of your Plan’s By-Law, and that if he doesn’t stop doing so the Owners Corporation will issue him with a Notice to Comply (with the By-Law).
As Cosmo said, if you don’t nip this in the bud it has the potential to become endemic, and that’s not desirable.
So far as any action against the Landlord is concerned, again, firstly find out if what the tenant said is true and maybe come back with another post at that time.