Hi * Maybe this is a stupid question but I just can not get it working. I have a page from which the user can view basic item data and which has a link to a page to display the bill of material of the item. <TD bgcolor="#97bae6" width="20%"> <dtml-with "_(abs_path=bmpsiq.absolute_url())"> <a href="&dtml-abs_path;?ps_par=<dtml-var pt_part>" target="main"> Stuklijst </a> </dtml-with> </TD> To get the bill of material I have the following sql method: <params>ps_par</params> select ps_comp, ps_start, ps_end from ps_mstr <dtml-sqlgroup where> <dtml-sqltest ps_par type=string op=eq> <dtml-and> <dtml-sqlgroup> ps_start = ? <dtml-or> ps_start <= today </dtml-sqlgroup> </dtml-sqlgroup> The dtml method to display the tree is : <dtml-let ps_comp=ps_par> <dtml-tree id=ps_comp branches_expr="ps_childLookup(ps_par=ps_comp)"> <b><dtml-var ps_comp></b> <dtml-var ps_start> </dtml-tree> </dtml-let> It works for the first time but when I try to expand it I get a key error on ps_par. What goes wrong?? Hope somebody can help Frans -- Frans C. H. Schneider <mailto:f.schneider@nido.nl> NIDO Universal Machines BV <http://www.nido.nl> Industriestraat 34 <mailto:info@nido.nl> PO Box 30 tel. +31 (0) 548 370 000 7450 AA Holten fax +31 (0) 548 370 233 the Netherlands