drag and drop cell from datagridview to another

You might need to change your codes to ::

 private void dataGridView1_MouseDown(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        DataGridView.HitTestInfo info = dataGridView1.HitTest(e.X, e.Y);
        if (info.RowIndex >= 0)
        {
            if (info.RowIndex >= 0 && info.ColumnIndex >= 0)
            {
                string text = (String)
                       dataGridView1.Rows[info.RowIndex].Cells[info.ColumnIndex].Value;
                if (text != null){
                     //Need to put braces here  CHANGE
                    dataGridView1.DoDragDrop(text, DragDropEffects.Copy);
                }
            }
        }
    }
}

 private void dataGridView2_DragDrop(object sender, DragEventArgs e)
{
    string cellvalue=e.Data.GetData(typeof(string)) as string;
    Point cursorLocation=this.PointToClient(new Point(e.X,e.Y));

    System.Windows.Forms.DataGridView.HitTestInfo hittest= dataGridView2.HitTest(cursorLocation.X,cursorLocation.Y);
    if (hittest.ColumnIndex != -1
        && hittest.RowIndex != -1){  //CHANGE
        dataGridView2[hittest.ColumnIndex, hittest.RowIndex].Value = cellvalue;
   }
}

private void dataGridView2_DragEnter(object sender, DragEventArgs e)
{
    e.Effect = DragDropEffects.Copy;
}

This part dataGridView1.DoDragDrop(text, DragDropEffects.Copy); of your code should be inside the braces as you are checking for a condition just prior to it, as (texts!=null)

You can use following code. I have tested it and it is working for copying cell data from one datagridview to another.

        private void dataGridView2_DragEnter(object sender, DragEventArgs e)
    {
        e.Effect = DragDropEffects.Copy;
    }

    /* Drag & Drop */
    private Rectangle dragBoxFromMouseDown;
    private object valueFromMouseDown;
    private void dataGridView1_MouseMove(object sender, MouseEventArgs e)
    {
        if ((e.Button & MouseButtons.Left) == MouseButtons.Left)
        {
            // If the mouse moves outside the rectangle, start the drag.
            if (dragBoxFromMouseDown != Rectangle.Empty && !dragBoxFromMouseDown.Contains(e.X, e.Y))
            {
                // Proceed with the drag and drop, passing in the list item.                    
                DragDropEffects dropEffect = dataGridView1.DoDragDrop(valueFromMouseDown, DragDropEffects.Copy);
            }
        }
    }

    private void dataGridView1_MouseDown(object sender, MouseEventArgs e)
    {
        // Get the index of the item the mouse is below.
        var hittestInfo = dataGridView1.HitTest(e.X, e.Y);

        if (hittestInfo.RowIndex != -1 && hittestInfo.ColumnIndex != -1)
        {
            valueFromMouseDown = dataGridView1.Rows[hittestInfo.RowIndex].Cells[hittestInfo.ColumnIndex].Value;
            if (valueFromMouseDown != null)
            {
                // Remember the point where the mouse down occurred. 
                // The DragSize indicates the size that the mouse can move 
                // before a drag event should be started.                
                Size dragSize = SystemInformation.DragSize;

                // Create a rectangle using the DragSize, with the mouse position being
                // at the center of the rectangle.
                dragBoxFromMouseDown = new Rectangle(new Point(e.X - (dragSize.Width / 2), e.Y - (dragSize.Height / 2)), dragSize);
            }
        }
        else
            // Reset the rectangle if the mouse is not over an item in the ListBox.
            dragBoxFromMouseDown = Rectangle.Empty;
    }

    private void dataGridView2_DragOver(object sender, DragEventArgs e)
    {
        e.Effect = DragDropEffects.Copy;
    }

    private void dataGridView2_DragDrop(object sender, DragEventArgs e)
    {
        // The mouse locations are relative to the screen, so they must be 
        // converted to client coordinates.
        Point clientPoint = dataGridView2.PointToClient(new Point(e.X, e.Y));

        // If the drag operation was a copy then add the row to the other control.
        if (e.Effect == DragDropEffects.Copy)
        {
            string cellvalue = e.Data.GetData(typeof(string)) as string;
            var hittest = dataGridView2.HitTest(clientPoint.X, clientPoint.Y);
            if (hittest.ColumnIndex != -1
                && hittest.RowIndex != -1)
                dataGridView2[hittest.ColumnIndex, hittest.RowIndex].Value = cellvalue;

        }
    }

The error is in this line:

Point cursorLocation = this.PointToClient(new Point(e.X,e.Y));

Because this. does not refer to the DataGridView, but rather to the Form.

It should be instead:

Point cursorLocation = dataGridView2.PointToClient(new Point(e.X,e.Y));