1. Suhosin settings incorrect:
Solution: ensure that you set suhosin.get. max_value_length to at least 2048, either via vhost.conf, .htaccess or php.ini. Create Hosting customers on the Magento Hosting Plan don't need to worry about this as Suhosin settings are already optimised for Magento.
php_value suhosin.get.max_value_length 2048 (if using .htaccess)
suhosin.get.max_value_length = 2048 (if using php.ini)
php_admin_value suhosin.get.max_value_length 2048 (if using vhost.conf)
2. Your firewall/proxy is blocking access to http://chart.apis.google.com/chart
Solution: allow access to http://chart.apis.google.com/chart in your firewall settings
3. Magento is trying to fetch the chart image through PHP (seems to affect some versions of Magento):
Solution: edit the file at app/design/adminhtml/default/default/template/dashboard/graph.phtml
Change: "getChartUrl(false)" to "getChartUrl(true)"
<p style=\"<?php echo $_containerStyle?>\"><img src=\"<?php echo $this->getChartUrl(true) ?> alt=\"chart\" title=\"chart\" /></p>
This will cause an SSL error to be displayed in Magento Admin however, so not ideal if you have SSL enabled in Admin.
4. The response from Google is taking to long to respond
Solution: edit your VPS/Server's /etc/resolv.conf file to use DNS servers closer to your server location. You will need to restart apache for those changes to take effect.
