Hi Sridhar,
Please check if in THE order business area 1000 is maintained. If PM order check business area at "Addit. Data" tab, if PP order check at "Assignment" tab.
Alternativey you can maintain substitutions for financial accounting in GGB1 wherein you can give substitution based on your logic.
e.g. if Plant = 1000 then substitute Business area = 1000
Reg, Rakesh