Membership subscription upgrades: "Upgrades not available"


I have the latest Membership Plugin installed and enabled. Supporter is also enabled.

I'm trying to test the ability of a Free User Subscriber to upgrade to a paying Membership subscription.

I login and go to the "renewal" page which has the [renewform]. The subscription upgrade buttons are marked "Upgrades not available". Why?

Is the renewal form the only way to request a subscription upgrade?

I have three subscription levels active and public. The Free User subscription is finite with the two paying subscriptions listed as serial. The Paypal gateway is active and Live. When a new user account is created and a Memblersip subscription is selected thye are taken to Payapl to complete the transaction, so this seems to be working.