Magento offers some nice charts and reports. Today we noticed an issue on client's back-end Magento dashboard, the turnover and order charts were not generated properly.
The answer to this problem is very simpel. If your server is behind a properly configured firewall it will probably block any request to unknown URLs. For example to URLs like: http://chart.apis.google.com/chart
In order to solve this problem you can consider to implement either of the 2 solutions below.