Error Messages In Membership Sign Up

I have a membership website. I have installed the latest Beta version at your suggestion in another thread.

I was testing the sign up process today and after filling out the form the subscription page shows these errors on the top of the page:

Subscribe

Warning: Cannot modify header information - headers already sent by (output started at /home/sisterh0/public_html/wp-content/themes/business-portfolio/template-fullwidth.php:7) in /home/sisterh0/public_html/wp-includes/pluggable.php on line 680

Warning: Cannot modify header information - headers already sent by (output started at /home/sisterh0/public_html/wp-content/themes/business-portfolio/template-fullwidth.php:7) in /home/sisterh0/public_html/wp-includes/pluggable.php on line 681

Warning: Cannot modify header information - headers already sent by (output started at /home/sisterh0/public_html/wp-content/themes/business-portfolio/template-fullwidth.php:7) in /home/sisterh0/public_html/wp-includes/pluggable.php on line 682

How can I fix this?

Thanks in advance. You always have answers.

JoAnn