Subscribe Shortcode with Pop up

I am using pop up pro which is a very nice pop up plugin by the way. I am trying to use it with the shortcode of Subscribe by email. I tried various combinations of Load PopUp using... and Form Submit settings. Most of the combinations will put a user in the Subscriber list but the email never gets sent it seems. Now, when I use Subscribe by Email shortcode on an actual page, it works with no issues... it's just when I try to put it on a popup. I would imagine that perhaps the popup for some reason or how the form is getting handled when it's in a pop up is messing something up. I'm thinking that I need to find the right combination of the 2 settings I mentioned above... I have tried about 10 combinations... rather than try another 20... maybe you guys already know what the answer is. And does the solution you have work if using the W3 Total Cache plugin. Thanks.