Trying to remove an Image from Imagelist

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C#

I have created an imagelist and listview programmatically and add a treeview in the win form. When the user will browse to an Image Root folder, it will create the listview and imagelist depending on the number of sub folder and also show the root folder and subfolders in the treeview. User will perform moving an image from the listview to the treeview. On my treeview_DragDrop event, when I call the File.Move() function, I get an error "The process cannot access the file because it is being used by another process". Which I understand the image in the imagelist need to be dispose and remove first. How can I dispose the object from the imagelist? Dispose and RemoveAt method are not working. here is the code snippet...

private void treeView1_DragDrop(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(typeof(ListViewItem)))
            {
                string DropInPath = string.Empty;
                string SelectedImage = string.Empty;
                ListViewItem li = (ListViewItem)e.Data.GetData(typeof(ListViewItem));
                TreeNode nodeToDropIn = this.treeView1.GetNodeAt(this.treeView1.PointToClient(new Point(e.X, e.Y)));
                if (nodeToDropIn == null) { return; }
                if (nodeToDropIn.Level > 0)
                {
                    try
                    {
                        DropInPath = nodeToDropIn.FullPath;
                        SelectedImage = SelectedFolder + "\\" + li.Text;
                        this.fldImageList.Images[li.Text].Dispose();
                        this.fldImageList.Images.RemoveAt(li.Index);
                        File.Move(SelectedImage, DropInPath);
                    }
                    catch (Exception ex)
                    {
                        MessageBox.Show(ex.Message);
                    }
                }

                if (li == null) { return; }
                nodeToDropIn.Nodes.Add(li.Text);
                fldListview.Items.Remove(li);
            }