Thanks for your explanations. I tried that and it worked as far as bringing the post that was not showing up.
However, when I added a reply to thread, I got the same error again
"No posts exist for this topic"

I checked that the poster_id for the last reply was indeed pointing to the userid of the person who added it (236).
I optimize the databse, and resync with no results.

1.) I optimize all the tables in database.
2.) I re-synch the forum

None of this solved the problem.

Inside phpbb forum administration, when I click on the first page of the thread, it displays fine: see below:
modules.php?name=Forums&file=viewtopic&t=7&start=0

BUT, the next page which really does not contain a posted test is the one that display the error:
modules.php?name=Forums&file=viewtopic&t=7&start=1 5

Any help on how to fix the problem with the thread?

Thanks,
dcasmr