Ok Rich, here is how I fixed it:
First I created a make table query. This make table query determines the number of replies for each topic, for each of the forums (in this case, just FORUM_ID=15):
SELECT FORUM_A_REPLY.TOPIC_ID, Count(FORUM_A_REPLY.REPLY_ID) AS CNT_REPLY INTO TempReply
FROM FORUM_A_REPLY
WHERE FORUM_A_REPLY.FORUM_ID=15
GROUP BY FORUM_A_REPLY.TOPIC_ID;
I do this in order to create an update query, linking the A_TOPICS table with this TempReply table, so that for each topic I can use the associated Reply count (CNT_REPLY). Here is the update query:
UPDATE FORUM_A_TOPICS INNER JOIN TempReply ON FORUM_A_TOPICS.TOPIC_ID = TempReply.TOPIC_ID
SET FORUM_A_TOPICS.T_REPLIES = TempReply.CNT_REPLY;
I executed the queries using TableEditor, in the order I'm presenting them now to you. That fixes the problem.
If you wanted to do this for other archived forums, you'd just need to remove or change the criteria for the first query.
I forgot to remove the TempReply table. Please do it, since there is no purpose in keeping it.