See the below for the error info ....

"nil is not a symbol"
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.3/lib/active_record/validations.rb:296:in `send'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.3/lib/active_record/validations.rb:296:in `validates_each'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.3/lib/active_record/validations.rb:514:in `validates_uniqueness_of'
#{RAILS_ROOT}/app/models/user.rb:25
#{RAILS_ROOT}/app/controllers/application.rb:29:in `check_authorization'
/usr/local/bin/mongrel_rails:18


in user.rb

  # Fun easy validation
  validates_uniqueness_of :username, :on => :createuser, :message => "is already in the system."
  validates_uniqueness_of :username, :on => :updateuser, :message => "is already in the system."
  validates_uniqueness_of :email, :on => :createuser, :message => "is already in the system."
  validates_uniqueness_of :email, :on => :updateuser, :message => "is already in the system."

	validates_format_of :username, :with => /^[A-Za-z][A-Za-z0-9\-\_]{2,39}$/, :message => "can only consist of letters, numbers, -, and _"
	validates_format_of :first_name, :with => /^[A-Za-z0-9\-\s]*$/, :message => "can only consist of letters, numbers, -, and _"
	validates_format_of :middle_name, :with => /^[A-Za-z0-9\-\s]*$/, :message => "can only consist of letters, numbers, -, and _"
	validates_format_of :last_name, :with => /^[A-Za-z0-9\-\s]*$/, :message => "can only consist of letters, numbers, -, and _"
  validates_format_of :email, :with => /^([^@\s] )@((?:[-a-z0-9] \.) [a-z]{2,})$/, :message => "is not valid."

  validates_length_of :email, :maximum=> 100, :message => "may only be a maximum of 100 charactars."
  validates_length_of :ip_address, :maximum => 15, :message => "is too long (format: ###.###.###.###)."
 	validates_length_of :first_name, :maximum => 40, :allow_nil => true
 	validates_length_of :middle_name, :maximum => 40, :allow_nil => true
  validates_length_of :last_name, :maximum => 40, :allow_nil => true

  validates_presence_of :username, :email, :ipaddr

  validates_numericality_of :confirmed, :on => :createuser
  validates_numericality_of :confirmed, :on => :updateuser





the newuser.rhtml

<h2><span>Create User</span></h2>

<%= start_form_tag({:action => "createuser", :controller => "admin"}, {:onSubmit => "Element.show('ident_spinner');" }) %>

	<%= render :partial => 'form_user' %>

<%= end_form_tag %>

the _form_user.rhtml

<script>keepFlashAlive = true;</script>

<!--[form:user]-->
<dl>

	<dt>Username</dt>
	<dd>
		<%= text_field 'user', 'username' %>
	</dd>

	<dt>Password</dt>
	<dd>
		<%= password_field 'post', 'password_first' %>
	</dd>

	<dt>Re-type Password</dt>
	<dd>
		<%= password_field 'post', 'password_second' %>
	</dd>

	<dt>Email Address</dt>
	<dd>
		<%= text_field 'user', 'email' %>
	</dd>

	<dt>First Name</dt>
	<dd>
		<%= text_field 'user', 'first_name' %>
	</dd>

	<dt>Middle Name</dt>
	<dd>
		<%= text_field 'user', 'middle_name' %>
	</dd>

	<dt>Last Name</dt>
	<dd>
		<%= text_field 'user', 'last_name' %>
	</dd>

	<br /><br />
	<dd>
		<input type='submit' value='Submit' class='primary' />
		<%= image_tag('/images/admin/spinner_mac.gif', :align => 'absmiddle', :border=> 0, :id=>'ident_spinner', :style=>'display: none;' ) %>
	</dd>

</dl>
<!--[eoform:user]-->

<%= params.inspect %>


the admin controller ....
  def newuser
    @user = User.new()
  end

  def createuser
    @user = User.new(params[:user])
    @user.password = params[:post][:password_first]
    @user.password_hash
    @user.password_salt
    if @user.save
      flash[:notice] = "The user was successfully created."
      redirect_to :action => "listusers"
    else
      render :action => "newuser"
    end
  end