This is most likely because the email address you are using is associated with an admin account. Admins cannot perform certain user interactions like donations, surveys, etc. including using "Tell-A-Friend". Test this functionality again with a user account and it will fix the issue most of the time.

Note that you don't have to be using your admin account for this to be a problem. Even if you send the email to a non-admin user if the email address is also associated with an admin account this may cause problems as well. This problem will occur whether the admin associated with that email address is active or not, so search C360 for the email address you used and make sure to check the box to include inactive constituents.