Error message: "Conversion failed when converting datetime from character string"

I am passing parameters to a stored proc and the asp.net code block is:
 
SqlConnection con = new SqlConnection(strConn); string sqlItemSearch = "usp_Item_Search"; SqlCommand cmdItemSearch = new SqlCommand(sqlItemSearch, con); cmdItemSearch.CommandType = CommandType.StoredProcedure; cmdItemSearch.Parameters.Add(new SqlParameter("@Item_Num", SqlDbType.VarChar, 30)); cmdItemSearch.Parameters["@Item_Num"].Value = txtItemNumber.Text.Trim(); cmdItemSearch.Parameters.Add(new SqlParameter("@Search_Type", SqlDbType.Int)); cmdItemSearch.Parameters["@Search_Type"].Value = ddlSearchType.SelectedItem.Value; cmdItemSearch.Parameters.Add(new SqlParameter("@Vendor_Num", SqlDbType.VarChar, 10)); cmdItemSearch.Parameters["@Vendor_Num"].Value = txtVendorNumber.Text.Trim(); cmdItemSearch.Parameters.Add(new SqlParameter("@Search_User_ ...