To use the Export to PDF functionality you have to add the Google Charts API into your Remote Site Settings in your organization.
To add a site to your Remote Sites, you have to go to: Setup > Security Controls > Remote Site Settings.
Click New Remote Site:
Remote Site Name: Google_Chart_Api
Remote Site URL: https://chart.googleapis.com
1. on the "Timba Surveys" tab select the "Analyze" Button.
2. Click on the "Export" button and select PDF Report