I feel your frustration. Been there so many times.
One thing that I like to do when a page isn't working, is to create a blank test page.
At the top add the error reporting and display function.
<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>
Now add one thing at a time starting with an echo like <?php echo "Hello World"; ?>.
Upload and open that page in your browser to make sure it's parsing correctly. Then add your connection above that. <?php require_once('Connections/jodenonline_i.php'); ?>
Save and refresh.
I'm guessing that this time you will see the error as before. Now focus just on that one thing.
You said that you checked the permissions and they were correct for the file and directory. And I assume you have double checked that the user in your connection script has permission to connect to the db? If those are all correct then it is most likely the path.
I would keep with Local Info > Links Relative to: > Document
One thing you can check as well, is if in Dreamweaver you right click on the <?php require_once('Connections/jodenonline_i.php'); ?> and select Open "Connections/jodenonline_i.php". If your path is wrong, it will not find the file. If it is correct, it should open your file in DW.
I know this is all basic boring stuff but it sometimes helps to try them.
TroyD