Hi,
Some of the sap standard fm modules for processing IDOC files internally use BDCs, the probl, is vth the bdc and it could be either missing data for the screen or it could also be a popup msz. u could also reprocess this idoc file via t/n code we19 instead of t/n code bd87. in t/n code we19 u should tell d system to process the idoc file in foreground and this should bring up the bdc screen.
hope it will be helpful.