wtashby:

At this point my best suggestion is to create a subdirectory on your site, and do a clean install of zencart there, install EP4 and see if it work normally.

You will have to create a separate database in CPanel. Be sure to also install Dr. Bytes MySQL Backup tool.

I'm sorry I can't offer a better solution. Returning to the core manual install often helps identify if the issue is server related or not.
This has been the case when someone used their CPanel auto installer to install Zencart instead of uploading the files and running the install manually.

-chadd