participant’s Database Plugin Giving Error on WPMU Dev Hosting

Hi,
I have support access on for autresearch.tempurl.com. A plugin, Participant’s Database is giving this error:
The configured uploads directory “/var/web/site/public_html/wp-content/uploads/participants-database/” for Participants Database is not writable. This means that plugins file uploads will fail, check the Participants Database “File Upload Location” setting for the correct path.