What are some causes to make the ENewsletter not to work in the Popup wpmudev plugin?

Hi:

What are some causes to make the ENewsletter not to work in the Popup wpmudev plugin?

It works everywhere else and also the Subscribe By Email plugin works in the Popup Pro as well.

The form shows up but nothing happens at all when the Subscribe button is clicked while inside the Popup Pro plugin.

Again, it works everywhere else...and Subscribe By Email works in the Popup Pro as well...

Greg