Quote Originally Posted by Sarah21 View Post
2. We tried swapping line 73, but that didn't resolve anything.
The errors in the logs you submitted yesterday were:
[21-Oct-2014 20:03:17 UTC] PHP Warning: Cannot modify header information - headers already sent by (output started at .../includes/languages/english/modules/shipping/canadapost.php:73) ...

That means there are unexpected characters in that file, including perhaps extra blank spaces/lines at the end of the file. It is explained further in this FAQ article: http://www.zen-cart.com/content.php?...s-already-sent

So, if your logs are still showing that error, and you have removed extraneous blank spaces/lines from/near line 73 in that file, then please post the entire contents of that file here so we can help you further.