Say for example ur 1st level WBS is DH/535/4001650ur 2nd level WBS element is DH/535/4001650/04Now look in table PRHI with posnr = DH/535/4001650/04u can see two fields UP = DH/535/4001650if anything below its showing in down.
Error would be always trapped whether synchronous or Asynchronous method ..So recording the BDC transaction u can do with the popups as any other screen sequence.