Well, it's fixed now.

I checked level 2 trace which showed identical output on both successful and unsuccessful inserts.
Then I changed the insert format as suggested by graff, along with using the prepare_cached method.

I believe the fault may have been as a result of my ugly insert syntax. Instead of using, INSERT INTO table (colums) VALUES (values), I was using, INSERT INTO table SET column1=value1, column2=value2. Not sure as to why there was a difference, but I am happy - for now - to accept it, but eventually would like to find out why no errors were created (is it DBI or the MySQL client/engine?).

Thank you to all who have read this post and especially to those who had the insight to post/cb.

Cheers!
matt