Apps 9 Report Rule ERROR Evaluating Expression

Want to set logical printer for INVENTORY_PART_BARCODE_REP using a Report Rule. Using the following expr1:

[&select inventory_location_api.get_location_group(ipis.contract, ipis.location_no) 
from inventory_part_in_stock ipis 
right outer join inventory_part_barcode ipb 
  on ipis.contract = ipb.contract 
  and ipis.part_no = ipb.part_no 
  and ipis.configuration_id = ipb.configuration_id 
  and ipis.lot_batch_no = ipb.lot_batch_no 
  and ipis.serial_no = ipb.serial_no 
  and ipis.eng_chg_level = ipb.eng_chg_level 
  and ipis.waiv_dev_rej_no = ipb.waiv_dev_rej_no 
  and ipis.activity_seq = ipb.activity_seq
where ipb.contract = '[@INVENTORY_PART_BARCODE_REP/BARCODE_LINES/BARCODE_LINE/CONTRACT]' 
and ipb.barcode_id = '[@INVENTORY_PART_BARCODE_REP/BARCODE_LINES/BARCODE_LINE/BARCODE_ID]']

Ordinal: 10

Operator: =

Expr: 100 

I get the following errors:

Rule ID=40 ORA-31011:ERROR Evaluating Expression=''[@INVENTORY_PART_BARCODE_REP/BARCODE_LINES/BARCODE_LINE/CONTRACT]'' result_key=538036formatter_properties=LocaleCountryGB

Rule ID=40 ORA-31011:ERROR Evaluating Expression=''[@INVENTORY_PART_BARCODE_REP/BARCODE_LINES/BARCODE_LINE/BARCODE_ID]'' result_key=538036formatter_properties=LocaleCountryGB

I have tested the SQL statement; it works… and I have tried removing all non essential spacing.

Any other ideas?