WordPress Custom Plugin – PHP file uploader in Top-Level Admin Menu – Page not found 404

This is my first Custom WordPress Plugin that I really need to get done. Been at this ALL night long and can’t figure out whats wrong… I’m assuming I’m missing something simple and basic with standard plugin coding.

I wrote a plugin that allows a Top-Level Menu item in the admin dashboard. Its a simple PHP upload form. All I want to do is let the client upload CSV files to a specific folder. I just tested the PHP code OUTSIDE of the wordpress framework and it works… But when I try and upload a file using the actual wordpress admin, I press submit and it doesnt upload the file it also sends me to a “page not found 404″… ON top of that when I activate the plugin on my production site it causes errors and some minor glitches… So I’m assuming I’m just missing some code I need in the plugin php file.

Here is the full code for my plugins main php file – minus the separate php file that handles all the “uploading code”

<?php
/*
Plugin Name: Points Uploader
*/
?>

<?php
add_action( 'admin_menu', 'sheets_plugin_menu' );

function sheets_plugin_menu() {
add_menu_page( 'Upload Points Sheets', 'Upload Points', 'manage_options', 'upload-   points-sheets', 'sheets_plugin_page', '', 10);
 }

function sheets_plugin_page() {
if ( !current_user_can( 'manage_options' ) )  {
wp_die( __( 'You do not have sufficient permissions to access this page.' ) );
}
echo '<div class="wrap">';
echo '<h1>Upload Points Sheets</h1>';
?>

<form action="uploader.php" method="post" enctype="multipart/form-data">
<label for="file">Select a file:</label> <input type="file" name="userfile" id="file">    
<br />
<button>Upload File</button>
</form>

<?php
echo '</div>';
}
?> 

So what do I need to add to this php page to make it a more “standard” operating plugin? When I press the submit button its like I’m missing a “wordpress send” code, and it just 404’s, I don’t know how to make it operate within the Admin screen field. Thank you for any help you can offer, I’m really stumped here. 😉

…ok just in case its needed here is the uploader.php file. Just a sample code I found on the net to test things out.

<?php
// Configuration - Your Options
$allowed_filetypes = array('.csv'); // These will be the types of file that will pass the validation.
$max_filesize = 524288; // Maximum filesize in BYTES (currently 0.5MB).
$upload_path = './upload/'; // The place the files will be uploaded to (currently a 'files' directory).

$filename = $_FILES['userfile']['name']; // Get the name of the file (including file extension).
$ext = substr($filename, strpos($filename,'.'), strlen($filename)-1); // Get the extension from the filename.

// Check if the filetype is allowed, if not DIE and inform the user.
if(!in_array($ext,$allowed_filetypes))
die('The file you attempted to upload is not allowed.');

// Now check the filesize, if it is too large then DIE and inform the user.
if(filesize($_FILES['userfile']['tmp_name']) > $max_filesize)
die('The file you attempted to upload is too large.');

// Check if we can upload to the specified path, if not DIE and inform the user.
if(!is_writable($upload_path))
die('You cannot upload to the specified directory, please CHMOD it to 777.');

// Upload the file to your specified path.
if(move_uploaded_file($_FILES['userfile']['tmp_name'],$upload_path . $filename))
echo 'Your file upload was successful, view the file <a href="' . $upload_path . $filename . '" title="Your File">here</a>'; // It worked.
else
echo 'There was an error during the file upload.  Please try again.'; // It failed :(.

?>