Page Not Found wiht basic form

I've been working on this module all weekend, and it was going great for a while, but now all I get is Page Not Found errors. I've stripped the module down to the basic form, but I still just get the same error. here's what I have:

<?php
//$Id$

/*
 * Adds the capability to assign access to projects
 * to specific users
 */

/*
 * Implementation of hook_menu()
 */
function project_permissions_menu($may_cache) {
  $items = array();
    if ($may_cache) {
      $items[] = array(
        'path' => 'admin/project/project_permissions',
        'title' => t('Project Permissions'),
        'description' => t('Set access to projects'),
        'access' => user_access('administer projects'),
        'callback' => 'project_permissions_page',
        'type' => MENU_NORMAL_ITEM
      );
    }
    return $items;
}

function project_permissions_page() {
  $output = t('This page is used to specify project permissions on a per-user basis');
  
  $output .= drupal_get_form('project_permissions_form');
  return $output;
}

/*
 * Define the project permissions settings form
 */
function project_permissions_form() {     
  $form['project_nid'] = array(
    '#type' => 'fieldset',
    '#title' => t('Project name title'),
    '#collapsible' => TRUE,
    '#collapsed' => FALSE,
  );  

  $form['project_nid']['projects'] = array(
    '#type' => 'textfield',
    '#title' => t('Project name'),
    '#maxlength' => 30,
    '#size' => 30,
    '#default_value' => $project_name,   
  );
  
  $form['project_nid']['users'] = array(
    '#type' => 'select',
    '#title' => t('Users with access to project'),
    '#description' => t('Select users to be assigned to the project'),    
    '#options' => _get_user_list(),
    '#multiple' => TRUE
  );
  
  $form['project_nid']['submit'] = array(
    '#type' => 'submit',
    '#value' => 'Submit'
  );    
  return $form;
}

I get the menu option just fine, but when I click on it, all I get is "Page Not Found." I'm following exactly an example in the Pro Drupal Development book, but it's not working. Can anyone explain why I would be getting this error?

Thanks.