Why do I get an error OLE IDispatch exception code 0 from Nodes: Element not found?

This is the code:

sele treeview
set multilocks on
=cursorsetprop("buffering",5,"treeview")

sele treeview
=tableupdate(.t.)
go top
o = thisform.oletreeview.nodes
o.clear

scan
	if alltrim(crelative) = '0'
		o.add(,1,alltrim(ckey),alltrim(ctext),0)
	else
erro >>>        o.add(alltrim(crelative),4,alltrim(ckey), alltrim(ctext),0)
	endif
endscan

thisform.oletreeview.selecteditem = thisform.oletreeview.nodes(1)

thisform.updateproperties(thisform.oletreeview.selecteditem)

if loexpand=0
	loexpand=1
else
	thisform.cmdexpandcollapse.click
endif

Please help me. TIA.