Thanks for stopping the error...... however (sorry)
1. It raises the same error on the table properties once you click on the table tab.
2. When you get the properties for the tr and td and probably table, the properties do not pick up what is in the html. e.g. the TD has the width and height and colour set but the dialog shows nothing set.
This is for IE 5.5 only it seems to work fine in the couple of others i tested.
Sorry