This looks like the error generated by MySQL. The code written by DataAssist will have the query to insert like this:
mysql_query(<query here>) or die(mysql_error());
If there's an error, then it displays the mysql_error(). If you wanted to output something other than the default mysql_error, you would want to check the mysql_errno() and output different messages based on the error number that is returned.
For that particular error, the error number is 1062:
As this is something that requires custom coding, it is not supported, so I can only point you in the right direction.