Why error:"Cannot create a child list for field TEST"

Question

In my class1.cs file,code for oracle connection is given below: public class Class1 { OdbcConnection orcn; string stringconn; string sql; DataSet dtst; OdbcDataAdapter dataadapt; public DataSet conn() { orcn=new OdbcConnection(); stringconn="DSN=orclconn;UID=scott;PWD=tiger;DRIVER={Microsoft ODBC for Oracle}; SERVER=adidas;"; orcn.ConnectionString=stringconn; sql="select * from test"; dataadapt=new OdbcDataAdapter(sql,orcn); dtst=new DataSet(); dataadapt.Fill(dtst); return dtst; } } In Form1.cs file, under Form_Load event,I have written: Class1 cc=new Class1(); ds=cc.conn(); int t=this.BindingContext[ds,"TEST"].Count; MessageBox.Show("t=",t.ToString()); When I try to compile, the following error occurs: "An Unhandled exception................................ Cannot create a child list for field TEST" What's is this error and how to resolve it.