Make sure the text format within input formats is set to full html within the forena configuration screen. Especially if you're planning to use SVG graphs it is important to avoid that tags are being stripped out, as this could cause such graphs to not be shown at all (or with some error messages).
As a variation, first define some new text format (e.g.: Reporting HTML) and then set the text format to this new text format. The advantage of using some new text format is that the impact of tuning the selected filter (as detailed below) will be limited to forena reports only.
Navigate to the configuration page related to text formats (within content authoring) and select the text format you specified on the forena configuration screen. Make sure these entries are turned of for the selected text format (within enabled filters):
Assuming you completed the setup of your SVG graph library, you should now be in good shape to start using forena's amazing charting features. To perform an easy validation about this, just checkout one of the SVG samples delivered with forena. Use the external SVG graph sample in case you're using an older browser that does not support inline SVG. Alternatively, if you're using a more recent browser, try using the Master Summary with drill down.
If you don't see a nicely formatted graph, but only some square with a grey background (about the size of the SVG graph you should see if it would have worked), or you're getting some error messages, you may want to checkout the issue queue on Drupal.org (search for html filter), such as in issue https://drupal.org/node/828458.