Strange problem with Word TOC

I am trying to create a table of contents in word 2003, and annoyingly got two entries for one heading. Any ideas on why it is happening and how I can remedy it? Many thanks.

 

The second heading has the same outline level designation to delete it press shift 9 to view the field code select the field code including the brakets and delete to hide codes press alt 9

 

Thanks for the info. I'll have a try with this solution next week.