Scripts

What could be causing RemoveObject to not work? Here's a snippet of the script:
function silF ()
if HasArtefact("Nadaur", 77) then
MessageBox("Maps/SingleMissions/Moon glade/derevo.txt");
PlayVisualEffect( "/Effects/_(Effect)/Spells/HolyWord.xdb#xpointer(/Effect)", "sil", 0, 0, 0, 6, 0 );
RemoveArtefact("Nadaur", 77);
SetObjectiveState("zadanie2", OBJECTIVE_COMPLETED);
sleep(2);
RemoveObject("ubr");
MessageBox("Maps/SingleMissions/Moon glade/sil.txt");
Trigger(OBJECT_TOUCH_TRIGGER, "sil", nil);
end;
end;
Trigger(OBJECT_TOUCH_TRIGGER, "sil", "silF");

Everything works except for the highlighted line. The object name is definitely correct. (The object was initially a tree, then I changed it to a structure, but it still doesn't work.)