Problem

The cronjob syncing data from Magento to Copernica starts, but never finishes. So no new data will be synchronised and my queue keeps getting larger. 

Solution

Add a file called test.php in the root of your Magento installation. Copy and past the code below and execute the php file. If the file executes well a start and endtime will appear. If anything goes wrong it will output the error or exception. 

test.php
<?php
require_once 'app/Mage.php';

ini_set('display_errors', 1);

umask(0);
Mage::app();

print 'Starttime:'. time();
print '<hr>';
$obj = Mage::getModel('marketingsoftware/observer');
$obj->processQueue();

print 'Endtime:'. time();
print '<hr>';