register_activation_hook problem

Hi, I have been getting the following message everyytime I try to activate my plugin:

Fatal error: Cannot redeclare phpbb3_integration_activate() (previously declared in /home/tyler/tylerc.org/area51/wordpress/wp-content/plugins/phpbb3.php:29) in /home/tyler/tylerc.org/area51/wordpress/wp-content/plugins/phpbb3.php on line 64

Here is my code:

<?php
/*
Plugin Name: phpBB3 Integration
Description: Integrates phpBB3 user database with WordPress user database.
Version: 1.0
Author: Tyler Cassidy
Author URI: https://www.tylerc.org/
*/

// Path to phpBB3 and WordPress directories
$phpbb3_path = '/home/tyler/http/area51/phpBB3/';
$wp_path = '/home/tyler/http/area51/wordpress/';

// Include phpBB3 / WordPress config file
include $wp_path . 'wp-config.php';
include $phpbb3_path . 'config.php';

$phpbb3_db = array(
'host' => $dbhost,
'user' => $dbuser,
'passwd' => $dbpasswd,
'name' => $dbname,
'prefix' => $table_prefix
);

// Plugin Activation Function and hook
function phpbb3_integration_activate()
{
  global $phpbb3_db;
  global $wpdb;

  $wp_table = $wpdb->prefix . 'users';
  $phpbb3_table = $phpbb3_db['prefix'] . 'users';
  $wp_sql = "SHOW TABLE STATUS FROM " . DB_NAME . " LIKE '" . $wp_table . "'";
  $phpbb3_sql = "SHOW TABLE STATUS FROM " . $phpbb3_db['name'] . " LIKE '" . $phpbb3_table . "'";

  $wp_con = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME);
  if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
  }
  $result = $wp_con->query($wp_sql);
  $row = $result->fetch_array(MYSQLI_ASSOC);
  $wp_insert_id = $row['Auto_increment'];
  $result->close();

  $phpbb3_con = new mysqli($phpbb3_db['host'], $phpbb3_db['user'], $phpbb3_db['passwd'], $phpbb3_db['name']);
  if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
  }
  $result = $phpbb3_con->query($phpbb3_sql);
  $row = $result->fetch_array(MYSQLI_ASSOC);
  $phpbb3_insert_id = $row['Auto_increment'];
  $result->close();

  if ($wp_insert_id < $phpbb3_insert_id)
    $wp_con->query("ALTER TABLE " . $wp_table . " AUTO_INCREMENT = " . $phpbb3_insert_id);
  if ($wp_insert_id > $phpbb3_insert_id)
    $phpbb3_con->query("ALTER TABLE " . $phpbb3_table . " AUTO_INCREMENT = " . $wp_insert_id);

  $wp_con->close();
  $phpbb3_con->close();
}
register_activation_hook(__FILE__, 'phpbb3_integration_activate');

?>

Would anyone happen to have any idea what is going on?

-Tyler