property Gantt.OLEDropMode as exOLEDropModeEnum
Returns or sets how a target component handles drop operations

TypeDescription
exOLEDropModeEnum An exOLEDropModeEnum expression that indicates the OLE Drag and Drop mode.
In the /NET Assembly, you have to use the AllowDrop property as explained here:

By default, the OLEDropMode property is exOLEDropNone. Currently, the ExGantt control supports only manual OLE Drag and Drop operation. Use the Background(exDragDropBefore) property to specify the visual appearance for the dragging items, before painting the items. Use the Background(exDragDropAfter) property to specify the visual appearance for the dragging items, after painting the items. Use the Background(exDragDropList) property to specify the graphic feedback for the item from the cursor, while the OLE drag and drop operation is running.  See the OLEStartDrag and OLEDragDrop events for more details about implementing drag and drop operations into the ExGantt control.