Invoke does not exist in the current context. The same method was not giving any error in Form.cs class but when I used in other class in same project it gives error. i am using threading on forms control.

private void UpdateText(object fileName)
        {
            if (Textbox.InvokeRequired)
            {
                UpdateTextCallback back = new UpdateTextCallback(UpdateText);
                this.Invoke(back, new object[] { fileName }); 
            }
        }