It is difficult to speculate about what the problem might be without having a look at the code. You state that an "empty space appears", which could indicate that the image is corrupt or completely transparent.

The following code sample demonstrates the correct approach; you could possibly compare this to your code and determine what is going wrong:

this.listView.View = UltraListViewStyle.Details;
this.listView.ViewSettingsDetails.ImageList = this.imageList1;

UltraListViewItem item = this.listView.Items.Add( null, "Test" );

// Assign the first member of the ImageList's Images collection
item.Appearance.Image = 0;

If this doesn't help, you might want to post a small code sample that demonstrates the problem, or report the issue via the web support form so that you can provide a test project that demonstrates the problem.