Error "You need to be running inside a web browser in order to submit this form"

Help! I'm brand new to creating forms. I have tried to copy the same settings that were on another form in my office that I know is working properly. I need to be able to list email addresses so that they receive the filled-in forms. I've tried using spaces, no spaces, commas, semicolons and if i compare to the other form, there are NO spaces and semicolons separating the email addresses. You can see from below what I've done, but then when I preview the form, this is the error I get. I don't know what I'm supposed to change, and ideally it would be nice if I DIDN'T have to "run this inside a web browser" in order to submit the form. I don't know whether or not the people filling it out will do that or not either, so the simpler, the better.