using if statement to compare a combo box value with two text boxes value

I'm using C# winforms I have a form with combobox called cmbExport and two textboxes txtDateSend and txtSendNum The combobox get its data from a stored procedure GET_ALL_EXPORT_WITHNULL

cmbExport.DataSource = cmp.GET_ALL_EXPORT_WITHNULL(); 
cmbExport.DisplayMember = "side";   
cmbExport.ValueMember = "ID_EXPORT";  
cmbExport.SelectedValue = "6";

When the user NOT choose certain values from the combobox and one of the textboxes are empty a meesage box appear

I tried this code but it didn't work:

int x = Convert.ToInt32(cmbExport.SelectedValue); //Its already integer but the code didn't accept int x = cmbExport.SelectedValue; ???

string ds = txtDateSend.Text;
string sn = txtSendNum.Text;

if ((x != 6 || x != 42 || x != 1042) && string.IsNullOrEmpty(sn))
    {
       MessageBox.Show("you should enter a send number");
       return;
    }
       else if ((x != 6 || x != 42 || x != 1042) && string.IsNullOrEmpty(ds))
    {
       MessageBox.Show("you should enter a date send);
       return;
    } 

thank you