Sorry, We had a Problem adding your email.

I was testing sendpress (using one of my email addresses) and received the following on the resulting webpage
Sorry, We had a Problem adding your email.
http://npscolorado.com/nps-program-news/?sendpress=post

But I received the email to opt-in just fine and then was sent to the custom thank you web page as I had expected.
http://npscolorado.com/newsty/

What am I missing?
http://www.npscolorado.com/

https://ww.wp.xz.cn/plugins/sendpress/