I had the same error; to fix it I modified the Admin.class.php file located in the directory at wp-content/plugins/exports-and-reports/wp-admin-ui/.
Look for this line:
$this->export_url = $this->base_url.'?download=1&_wpnonce='.wp_create_nonce('wp-admin-ui-export').'&export=';
Below that line I added the following (using mysite.com for this example):
$this->myexport_url = 'http://mysite.com/wp-content/exports/';
Then I took this block for each file type (CSV, XML, JSON, etc…CSV block featured here)
$this->message('<strong>Success:</strong> Your export is ready, the download should begin in a few moments. If it doesn\'t, <a href="'.$this->export_url.urlencode($export_file).'" target="_blank">click here to access your CSV export file</a>.<br /><br />When you are done with your export, <a href="'.$this->var_update(array('remove_export'=>urlencode($export_file),'action'=>'export')).'">click here to remove it</a>, otherwise the export will be deleted within 24 hours of generation.');
echo '<script type="text/javascript">window.open("'.$this->export_url.urlencode($export_file).'");</script>';
And replaced each instance of this:
.$this->export_url.urlencode($export_file)
With:
.$this->myexport_url.urlencode($export_file)
So it ended up looking like this:
$this->message('<strong>Success:</strong> Your export is ready, the download should begin in a few moments. If it doesn\'t, <a href="'.$this->myexport_url.urlencode($export_file).'" target="_blank">click here to access your CSV export file</a>.<br /><br />When you are done with your export, <a href="'.$this->var_update(array('remove_export'=>urlencode($export_file),'action'=>'export')).'">click here to remove it</a>, otherwise the export will be deleted within 24 hours of generation.');
echo '<script type="text/javascript">window.open("'.$this->myexport_url.urlencode($export_file).'");</script>';
Hope this helps!
