problem in b d c

hi friends, i am developing a BDC for account master using table SKA1 with field XBILK and transaction codes fs00 and fb01. in program i am not supposed to get any pop up screen when XBILK is 'X.' for cost center data entry i.e when XBILK is X no cost center will be there, but i am getting pop up screen asking me to enter costcentre even it is X . please suggest me in this regard. it s urgent. due to some reasons i can't sending the code.

kumar.