One thing that I do quite often when there is an issue with what data is available at a certain scope is to replace the template/section with something like:
<div data-bind="text: ko.toJSON($data)"></div>
Or, if you want a slightly more readable version:
<pre data-bind="text: JSON.stringify(ko.toJS($data), null, 2)"></pre>
This will spit out the data that is being bound at that scope and let you make sure that you are nesting things appropriately.
Update: as of KO 2.1, you can simplify it to:
<pre data-bind="text: ko.toJSON($data, null, 2)"></pre>
Now the arguments are passed on to JSON.stringify.