Hello Nigel and Fabricio found another error. When TImageEnMView ScrollBars equals ssHorizontal and MouseInteract = mmiScrool, the scroll bar does not work. You can verify this?
This can not be verified here. When ScrollBars = ssHorizontal and MouseInteract = [mmiScroll] the scrollbar becomes visible when the total width of the thumbnails exceeds the ClientWidth of TImageEnMView. Scrolling the images also works as expected.