Cecilia says:Chris, sorry to disagree with you, but I do think it is a "new user" issue....
I created an account to a friend of mine and I wasn't able to add a run manually. And in the very same browser I am able to add a run manually to my account.
So I synchronized his account with my Nike plus account,then added a new run manually and deleted my runs to get it working for him. :S Of course that's not a good solution, but was the only one I had.
Have a good weekend!