Hi,
It could be possible that XYToNode is returning nil, so I would assign this value to a private variable before accessing the FileName
var
d: TAdvDirectoryTreeViewNode;
begin
d := TAdvDirectoryTreeViewNode(tvDokumente.XYToNode(AuftragX,AuftragY).Node);
if Assigned(d) then
filename:=d.FileName;
end;