customer mastersata external bp number in idetification tab

hi,

iam dowm loading data from flat file to crm.

iam using bapi_bupa_create_from_data.

bapi_bupa_add_roles.

commit.everything is working perfectly.

but i need to pass one parameter i.e in identification tab

"bussiness partner external number".

iam adding search1 and search2 and place it in bp external number.

how to give this parameter.which function module should i use.

If i use bapi' bapi_bupa_create_fromdata.and parameter is bussinesspartnerexternno run time error occuring.

how can i fill bpexternalnumber in identification tab in bp master data...

please help me.