Bdc: In Bdc if i maintain a flat file in appilcation server

Hi abapers

1. In Bdc if i maintain a flat file in appilcation server., which one i need to be uploaded , i will give the file name in selection-screen of bdc program, accidentally

i will give wrong file name ,i.e which is not there , how to check wheather i entered correct file name or not.............

waiting for answers

with Regards

Bhaskar Rao.M