PayPal Subscription Error Message

Hi

I have successfully installed the membership plug-in, set-up free and pay for premium levels (annual subscription) and all is working fine. PayPal Express Gateway Add-On has been activated and the Payment Gateways >> PayPal Express – with Subscriptions is activated. The issue I have is with the Step 2: Select a Subscription step in the sign-up process. The page says:

STEP 2. SELECT A SUBSCRIPTION

Please select a subscription from the options below.

The paid subscription level is listed with the PayPal Subscribe button.

However, when I click on the Subscribe button, I’m taken to the PayPal page but am given the following error message.

“Invalid Regular period. You must specify valid values for the A3, P3, and T3 parameters for a subscription.”

Any help would be appreciated. Thanks in advance.