Custom control Properties

[SLH]

Thanks for your reply.

I've changed the code as per your recommendations, listed below:

public class LoginControl : System.Web.UI.WebControls.WebControl
 	{
 		private const string _usernameStateKey = "usrnm";
 		private const string _passwordStateKey = "pswrd";
 
 		private string _username;
 		private string _password;
 		
 		private System.Web.UI.WebControls.TextBox txtusername = null;
 		private System.Web.UI.WebControls.TextBox txtpassword = null;
 		private System.Web.UI.WebControls.Button cmdLogon = null;
 		private System.Web.UI.WebControls.RequiredFieldValidator reqUsername = null;
 		private System.Web.UI.WebControls.RegularExpressionValidator revPassword = null;
 
 		[Bindable(true),Category("TextBoxContents")]
 		public string Username
 		{
 			get
 			{
 				if (ViewState[_usernameStateKey] != null)
 		    		return (string)ViewState[_usernameStateKey];
 				else
 					return _username;
 			}
 			set
 			{
 				_username = value;
 				ViewState.Add(_usernameStateKey,value);
 			}
 		}
 		public string Password
 		{
 			get
 			{
 				if (ViewState[_passwordStateKey] != null)
 		    		return (string)ViewState[_passwordStateKey];
 				else
 					return _password;
 			}
 			set
 			{
 				_password = value;
 				ViewState.Add(_passwordStateKey, value);
 			}
 		}
 
 		public new void PreRender()
 		{
 			EnsureChildControls();
 		    txtusername.Text = ViewState[_usernameStateKey] == null ? _username : (string) ViewState[_usernameStateKey];
 		    txtpassword.Text = ViewState[_passwordStateKey] == null ? _password : (string) ViewState[_passwordStateKey];
 		}
 
 		protected override void CreateChildControls()
 		{
 			txtusername = new TextBox();
 			txtpassword = new TextBox();
 			cmdLogon = new Button();
 			reqUsername = new RequiredFieldValidator();
 			revPassword = new RegularExpressionValidator();
 			txtusername.ID = "txtusername";
 			
 			txtpassword.TextMode = TextBoxMode.Password;
 			cmdLogon.Text = "Logon";
 			txtusername.Width = 140;
 			txtpassword.Width = 140;
 			txtusername.MaxLength = 15;
 			txtpassword.MaxLength = 15;
 			txtpassword.TextMode = TextBoxMode.Password;
 			txtpassword.ID = "txtpassword";
 
 			cmdLogon.Text = "Logon";
 			cmdLogon.Attributes.Add("OnServerClick","Submit_Click");
 			
 			reqUsername.Display = ValidatorDisplay.Dynamic;
 			reqUsername.EnableClientScript = true;
 			reqUsername.ErrorMessage = "Username must not be blank";
 			reqUsername.ControlToValidate = "txtusername";
 
 			revPassword.Display = ValidatorDisplay.Dynamic;
 			revPassword.EnableClientScript = true;
 		    revPassword.ErrorMessage = "Password must be at least 6 alpha-numeric charactors";
 			revPassword.ControlToValidate = "txtpassword";
 			
 			this.Controls.Add(txtusername);
 			this.Controls.Add(txtpassword);
 			this.Controls.Add(reqUsername);
 			this.Controls.Add(revPassword);
 		}
 		
 		/// <summary>
 		/// Render this control to the output parameter specified.
 		/// </summary>
 		/// <param name="output"> The HTML writer to write out to </param>
 		protected override void Render(HtmlTextWriter output)
 		{
 			output.Write("<table border=\"1\" width=\"300\" id=\"table1\">");
 			output.Write("<tr border=\"0\">");
 			output.Write("<td border=\"0\">Username:</td>");
 			output.Write("<td border=\"0\">");
 			txtusername.RenderControl(output);
 			output.Write("</td>");
 			output.Write("</tr>");
 			output.Write("<tr border=\"0\">");
 			output.Write("<td border=\"0\">Password:</td>");
 			output.Write("<td border=\"0\">");
 			txtpassword.RenderControl(output);
 			output.Write("</td>");
 			output.Write("</tr>");
 		    output.Write("<tr border=\"0\"><td colspan=\"2\"><div align=\"centre\">");
 			cmdLogon.RenderControl(output);
 			output.Write("<br>");
 			reqUsername.RenderControl(output);
 			output.Write("<br>");
 			revPassword.RenderControl(output);
 			output.Write("</div></td></tr>");
 			output.Write("</table>");
 		}
 	}

However, i still get the same problem, except that now if i change the property at design time, when running it i get an object reference not set error.

Any help would be greatly appreciated.