Fuel_sitevariables_model.php

almostcompletely

public function retrieve_one($name = null)
{
    $vars = $this->find_one_array(array('active' => 'yes', 'name' => $name));
    return $vars['value'];
}

Returns an error if $vars is empty (ie. if named variable is set to inactive).

Try this instead:

return (!empty($vars))?$vars['value']:'';

admin

This has been pushed to the develop branch:
https://github.com/daylightstudio/FUEL-CMS/tree/develop