Subscribe by Email Error When Sending to a Larger List

I am trying to send to a list of about 1,200. I tested the plugins sending it to about 30 people and it sent fine. FYI, I have it set to send out immediately upon posting. When I added about 1,200 subscribers I get the following error every time I hit publish:

Fatal error: Cannot use string offset as an array in /home/.../public_html/wp-content/plugins/subscribe-by-email/model/model.php on line 457

The post gets published, but the email doesn't go out. I checked the sent statistics and it says it sent to "0" subscribers. Please let me know a fix.