I was able to get the treelist working by setting my DataSource as follows:
.DataSource(d => d .ServerOperation(true) .Model(m => { m.Id(f => f.Id); m.OrderId(f => f.OrderId); m.ParentId(f => f.ParentId); }) .Read(read => read .Action("ReadTasks", "MyGanttController") ) )Will try using Guid.ToString() again as this is working for ints.