Wordpress on Zencart - Header error on a few pages, but not others

Yes, I know that the there is a post dedicated to the Zen Cart/Wordpress addon, but I feel that the issues/solutions are becoming too difficult to navigate through that.

My site (blackcuproaster.com) has all the layout/look I have been looking for with the wordpress blog being presented on the homepage and other aspects. I am running into a common issue of an error code popping up only on certain pages:

http://www.blackcuproaster.com/
http://blackcuproaster.com/index.php?main_page=index (after logging in, it is directed to this)

The error is the following:
Warning: Cannot modify header information - headers already sent by (output started at /home/content/t/b/c/tbcroaster/html/includes/templates/template_default/common/html_header.php:22) in /home/content/t/b/c/tbcroaster/html/wp/wp-includes/pluggable.php on line 865

I have done everything from change my htaccess to push anybody that goes to https://www.blackcuproaster.com to blackcuproaster.com, but that has errored out with every code made. I have talked to tech support from GoDaddy (I know, but I didnt make the decision, the boss did) and they said they couldnt do anything with the forwarding. It was bringing up the same issue that I was having.

As for the full on error code, I have also attempted every fix that I could find in these forums and others and am at a loss of what to do. I would really love to have some help with this issue so I might get it fixed for good. Anything would be great.

Thank you in advance.