Hi Tim
Try this:
In the RoboHelp HTML Explorer pane (the left pane) expand
your Single-Source Layouts pseudo folder.
Right-click your Microsoft HTML Help layout and select
Properties from the context menu.
On the properties dialog, click the Advanced... button.
Now click the TOC Styles tab.
Click to place a check mark in the attribute labeled
"Plus/Minus Squares".
Click OK until all dialogs are dismissed.
Re-compile your project and test.
Hope this helps... Rick