SuccessMessage and ConditionalErrorMsg printing at the same time

Hi;

If duplicate record found. The page printing firstly SuccessMessage then printing ConditionalErrorMsg.

I expecting that if duplicate message found only print ConditionalErrorMsg.

This is because InsertPermission setted to False but not work I think.
if (mysql_num_rows(mysql_query($QueryForCheckDuplicate)) == 0) {
$InsertPermission = "True";
}
else {
$InsertPermission = "False";
}