Blank lines on every page

I am trying to install Stamps.com and have worked closely with their support team. The error that is preventing the proper functioning of this add-on relates to 4 BLANK lines at the beginning of every page on the site. I can see the lines using firebug, but don't know which file is causing them.
I am trying to REMOVE these lines but can't seem to locate them in the header and main_page php files, for templates, common and default folders.
I am using version 1.3.8a of Zen Cart.
The website is https://www.pranajewelry.com.

Any suggestions on which files in order of precedence and what special code I should look for?

Thanks in advance for your help!
Dean

Hello,

Thank you for the message. We are working to determine a solution for the error that you are receiving and should be able to provide an answer soon.

Thanks!
Chuck
Stamps.com