Shop - Notifications page in admin=error 500 - Click Buy button=blank page

Hi,

Shop giving errors:
In admin cannot reach "notifications page" we get browser alert: HTTP 500 error

On shop online page - clicking the "Buy" button (shop.php?action=checkout) here in Spanish (Concluir Pago) presents a blank page
http://sociedaddominicanadepsiquiatria. ... cuotas.php

Tried full download (shift+update)
Tried to create a test shop (zero formatting) - same issue
http://sociedaddominicanadepsiquiatria. ... t_shop.php

Hopefully you can provide some assistance.

Note these 2 problems were present before 4.4.04 update (so issue is not related to last update)

Thank you.

PS: Sent Admin & FTP login to email