Conversion failed when converting date and/or time from character string.

string s = "SELECT user_name FROM login WHERE user_name = @u"; // there are no apostrophes around %u!
SqlCommand cmd = new SqlCommand(s, con);
cmd.Parameters.AddWithValue("@u", Label1.Text);

tried this worked fine . thnk you all


DateTime datetime = Convert.ToDateTime(Date.Text);
            SqlCommand cmnd = new SqlCommand("SELECT * FROM  Tech_data where Call_assign= @Call_assign and dateadd(dd, datediff(dd,0, [date_time]), 0) = @date_time ");
            cmnd.Connection = con;
            cmnd.Parameters.Add("@Call_assign", SqlDbType.VarChar).Value = Label1.Text;
            cmnd.Parameters.Add("@date_time", SqlDbType.DateTime).Value = datetime.Date;
            SqlDataAdapter da = new SqlDataAdapter(cmnd);
            DataSet ds = new DataSet();
            da.Fill(ds);

If the problem persists while executing your code, perhaps it is due to two important reasons:

1. Yo have used the ' DateTime.Now.ToShortString' or similar auto conversion method, and
2. You changed the computers default Datetime format in the setting.

Change the Datetime format of the computer or change the autoconversion to 'parse' method.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace InventoryStock
{
    public partial class Workstations : Form
    {
        public Workstations()
        {
            InitializeComponent();
        }

        private void label1_Click(object sender, EventArgs e)
        {

        }

        private void label1_Click_1(object sender, EventArgs e)
        {

        }

        private void Workstations_Load(object sender, EventArgs e)
        {
            comboBox3.SelectedIndex = 0;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            
            SqlConnection con = new SqlConnection(@"Data Source=sh-jasonk\dev;Initial Catalog=ITInventory;Integrated Security=True");
            //Insert Logic
            con.Open();
            bool Wkst_Status = false;
            if (comboBox1.SelectedIndex == 0)
            {
                Wkst_Status = true;
            }
            else
            {
                Wkst_Status = false;
            }
            
            SqlCommand cmd = new SqlCommand(@"INSERT INTO [dbo].[Workstations]
           ([Emp_Id]
           ,[Emp_Name]
           ,[Emp_Surname]
           ,[Department]
           ,[Company]
           ,[Hostname]
           ,[Wkst_Status]
           ,[Make]
           ,[Model]
           ,[SerialNumber]
           ,[ProductNumber]
           ,[Purch_Date]
           ,[WExpiry_Date]
           ,[Memory]
           ,[Processor]
           ,[HDD]
           ,[OS])
          
     VALUES
           ('" + Emp_ID.Text + "','" + txtName.Text + "','" + txtSurname.Text + "','" + comboBox1.Text + "','" + comboBox2.Text + "','" + txtHostName.Text + "','" + comboBox3.SelectedIndex + "','" + txtMake.Text + "','" + txtModel.Text + "','" + txtSN.Text + "','" + txtPN.Text + "','" + dateTimePicker1.Text + "','" + dateTimePicker2.Text + "','" + txtMem.Text + "','" + txtProc.Text + "','" + txtHDD.Text + "','" + txtOS.Text + "')",con);
          
            //Conversion failed here
            cmd.ExecuteNonQuery();
            con.Close();
            DateTime datetime = Convert.ToDateTime(dateTimePicker1.Text);
            //Reading Data
            SqlDataAdapter sda = new SqlDataAdapter("Select * From [dbo].[Workstations]", con);
            DataTable dt = new DataTable();
            sda.Fill(dt);
            dataGridView1.Rows.Clear();

            foreach (DataRow item in dt.Rows)
            {
                int n = dataGridView1.Rows.Add();
                dataGridView1.Rows[n].Cells[0].Value = item["Emp_Name"].ToString();
                dataGridView1.Rows[n].Cells[1].Value = item["Emp_Surname"].ToString();
                dataGridView1.Rows[n].Cells[2].Value = item["Department"].ToString();
                dataGridView1.Rows[n].Cells[3].Value = item["Company"].ToString();
                dataGridView1.Rows[n].Cells[4].Value = item["Hostname"].ToString();
                if ((bool)item["Wkst_Status"])
                {
                    dataGridView1.Rows[n].Cells[5].Value = "Active";
                }
                else
                {
                    dataGridView1.Rows[n].Cells[5].Value = "Inactive";
                }

              
                dataGridView1.Rows[n].Cells[6].Value = item["Make"].ToString();
                dataGridView1.Rows[n].Cells[7].Value = item["Model"].ToString();
                dataGridView1.Rows[n].Cells[8].Value = item["SerialNumber"].ToString();
                dataGridView1.Rows[n].Cells[9].Value = item["ProductNumber"].ToString();
                dataGridView1.Rows[n].Cells[10].Value = item["Purch_Date"].ToString();
                dataGridView1.Rows[n].Cells[11].Value = item["WExpiry_Date"].ToString();
                dataGridView1.Rows[n].Cells[12].Value = item["Memory"].ToString();
                dataGridView1.Rows[n].Cells[13].Value = item["Processor"].ToString();
                dataGridView1.Rows[n].Cells[14].Value = item["HDD"].ToString();
                dataGridView1.Rows[n].Cells[15].Value = item["OS"].ToString();
            }

        }
    
        private void label17_Click(object sender, EventArgs e)
        {

        }
    }
}