Hi,
Assuming s your on bw 7.x version.
At bw side, use table - RSOSFILEDMAP,
try to see the above table content, use FIELDNM - bbnull and execute it.
like same you can do for another field. if any bw objects exist it may shows under IOBJNM column.
if not then you need to go with custom info object same type and length of source field.
Thanks