The document may be corrupted. Try saving as an IDML (File > Save As > InDesign CS4 or later (IDML)). Reopen.
Look at it in Story Editor view to see if the text is still there.
Display hidden characters.Look for a break character.
See if a style has a break assigned.
Is your TOC going into its own frame?
Thanks Jane we did go through a lot of troubleshooting and the Adobe technician brought it down to a corrupt file
Is it solved yet, then?
Steve's suggestion of saving to idml usually works.
It could be a font or something on one page, such as an image. So sometimes copying the pages to a new document works. Do half, if that fails, do half of that, and so on. Use the pages panel menu.
What we’ve ended up doing was: created a new document with the same specs as the original and did a Move Pages (the entire document into the new one) and the TOC worked fine and there was no further problems at all.
Thanks Steve, I did reply to you earlier but didn’t Add Reply to my comments so they were not posted. See what we did as a solution above.