It looks like dataGridView1.DataSource is not of type DataTable.
If dataGridView1 is bound to a DataSet, DataTable or DataView the following code should work
var cm = (CurrencyManager)dataGridView1.BindingContext[dataGridView1.DataSource, dataGridView1.DataMember];
var dataView = (DataView)cm.List;
dataView.RowFilter = string.Format("Name='{0}'", textBox2.Text);