PayPal sandbox IPN successful, gateway transaction log correct, but subscription not applied

Hi,

My site isn't successfully applying subscriptions to users once they've completely passed through the paypal sandbox. The payment goes perfectly, for the correct amount with the correct description, but once they're back on the site they stil have no subscription. In the gateway log, completed payments show up with all information complete - username, transaction ID, date, etc.

Additionally weird and possibly related, I can't apply subscriptions from the dashboard, either. When I click 'add' in the user's row under 'subscriptions', I select the one to add, but it doesn't appear. when I return to the member.

It might help to check logs if they exist, but I can't see any in the plugin directory - is there a log somewhere?

I'm really pushing for a launch tonight, so I would very, very much appreciate some prompt assistance here. Thank you for your time!