got error while datareader operation.

Question

here i got error while get declare a value in label4.text = dr.GetString(11);

Error is: 

System.InvalidOperationException: Invalid attempt to read when no data is present. at System.Data.SqlClient.SqlDataReader.ReadColumn(Int32 i, Boolean setTimeout) at System.Data.SqlClient.SqlDataReader.GetString(Int32 i) at Login.userLogin_Click(Object sender, EventArgs e) in d:\TEST\attend\Login.aspx.cs:line 47

but i declare a value in that field but still get error here., advance thanks..