Errors in c#

Thank you all for your idea , i got the solution for that trouble , the problem is that a control in the solution has not been built.

Nothing happened until i used some trial dotnetbar tools this morning .
Below is one of my classes  , In Form1 , I declare an object textbox named textbox1 on this class and The error was shown .
 public class MyNumText : DevComponents.DotNetBar.Controls.TextBoxX 
    {
        protected override void  OnTextChanged(EventArgs e)
        {

//            TextBox t = (TextBox)sender;

            if (this.Tag != null && this.Tag.ToString() == "0") return;
            String Text = this.Text;
            int selStart = this.SelectionStart;
            int commaCount_Before = 0;
            int commaCount_After = 0;
            for (int i = 0; i < Text.Length; i++)
            {
                if (Text.Substring(i, 1) == ",")
                {
                    commaCount_Before++;
                }
            }
            Decimal Num;
            Text = Text.Replace(",", "");
            if (Decimal.TryParse(Text, out Num))
            {
                Text = String.Format("{0:N0}", Num);
                this.Text = Text;
            }
            for (int i = 0; i < Text.Length; i++)
            {
                if (Text.Substring(i, 1) == ",")
                {
                    commaCount_After++;
                }
            }
            int diff = (commaCount_After - commaCount_Before);
            if (diff >= 0)
            {
                this.SelectionStart = selStart + (commaCount_After - commaCount_Before);
            }
            base.OnTextChanged(e);

        }

        protected override void  OnLeave(EventArgs e)
        {
            String Text = this.Text.Replace(",", "");
            int Num;
            if (int.TryParse(Text, out Num))
            {
                Text = String.Format("{0:N0}", Num);
                this.Text = Text;
            }
            base.OnLeave(e);

        }

        protected override void  OnKeyDown(KeyEventArgs e)
        {
            //TextBox t = sender as TextBox;
            bool FirstTime = false;
            if (e.KeyCode == Keys.Delete || e.KeyCode == Keys.Back)
            {
                if (this.Text.Contains(",") == true)
                {
                    FirstTime = true;
                }
                else
                {
                    return;
                }
            }
            if (e.KeyCode == Keys.Back)
            {
                int commaCount = 0;
                this.Tag = "0";
                int selStart = this.SelectionStart;
                for (int i = 0; i < selStart; i++)
                {
                    if (this.Text.Substring(i, 1) == ",")
                    {
                        commaCount++;
                    }
                }
                this.Text = this.Text.Replace(",", "");
                selStart -= commaCount;
                if (selStart >= 0)
                {
                    this.SelectionStart = selStart;
                }

            }
            else if (e.KeyCode == Keys.Delete)
            {
                int commaCount = 0;
                this.Tag = "0";
                int selStart = this.SelectionStart;
                for (int i = 0; i < selStart; i++)
                {
                    if (this.Text.Substring(i, 1) == ",")
                    {
                        commaCount++;
                    }
                }
                this.Text = this.Text.Replace(",", "");
                selStart += commaCount;
                selStart -= 3;
                if (selStart >= 0)
                {
                    this.SelectionStart = selStart;
                }
            }
            else
            {
                this.Tag = "";
            }

            if (FirstTime)
            {
                e.Handled = true;
                return;
            }
            base.OnKeyDown(e);
        }
    }  // Text box kieu so

Hi,
U need to share ur class and form code to get an idea

I downloaded new components from Dotnetbar tools this morning and the errors can come from it . But i had used Dotnetbar component ( not full ) without error .

Look at the references of your project. Click on References node in Solution Explorer. You will see some errors in some assemblies referenced in your project. You need to either install them or readd them by deleting and adding the back (if they are locally stored in your project's bin folder).
You may also be using a different version of a product.