Hi,
There are a few JTreeTable implementations out there - so, you need to let us know which one you are using. Most people use the 'original' JTreeTable - an article written on Sun in 2000 or so.
There is also the SwingX JTreeTable and Netbeans Outline (ETable)...
Specifically, make sure your implementation of getChild(), getChildCount() and getIndexOfChild() methods of TreeTableModel is correct.
Try to create a simple example and post the
sscce.