[satiss7pwr]

public CheckBox[] cb = null;
int z=0;
protected void Page_Load(object sender, EventArgs e)
	{
		if (!IsPostBack)
		{
		   int count = (int)countcmd.ExecuteScalar();
		   Int32 k = Convert.ToInt32(Session["TZ"]);

			cb = new CheckBox[count - k];

		   OleDbCommand cmd = new OleDbCommand("Select   Member_Name from Member_Master", con);
			dr = cmd.ExecuteReader();
			
			
			while (dr.Read())
			{
			
			 //creating check box 
			  
			  
					cb[z] = new CheckBox();
					cb[z].Text = dr["Member_Name"].ToString();
					Panel2.Controls.Add(cb[z]);
					Panel2.Controls.Add(new LiteralControl("</br>"));
					// if (z == (t - 1)) { Button6.Visible = true; }
					z = z + 1;
			  
			}
		}
	}
protected void Button6_Click(object sender, EventArgs e)
{
	  //proccess to get the value of checked box and insert into database
		cb[tzx] = new CheckBox();
	
		for (int x = 0; x < cb.Length; x++)//ERROR OOCUR HERE
		{
			//cb[x] = new CheckBox();
			if (cb[x].Checked == true)
			{
	
					   //remain code..
			  
			}
		}
		
	}

[eclipsed4utoo]

1. you should learn to use the CODE tags


2. This seems to be a common mistake. Remember that ASP.Net runs ALL code outside of event handlers and methods. So this code...

public CheckBox[] cb = null;
int z=0;

is executed on EVERY postback. Therefore, when you click a button, the checkbox array is being set to null.

To persist data across postbacks, you can use the Session.

It seems that you only "create" the checkbox array on the first load of the page, though it's kind of hard to tell since your code isn't formatted.