Fatal error in Elis 2.7 on Sync custom fields

When I try to sync the user fields I get this error:
http://elis.dev/local/elisprogram/index.php?s=field&action=forceresync

```
Please wait. Resynchronizing data with Moodle.
Fatal error: Class 'user' not found in /var/www/vhost/local/eliscore/fields/moodleprofile/custom_fields.php on line 298
```
- PHP 5.5.30
- opcache enabled 
- Apache 2.2.15
