Error file generation using BDC

Hi .. friends . This is Sudhir . I have a scenario of loading 50 materials using BDC concept (generate session method) with tcode mm01. During loading if we have any faulty materials then they have to be written in a separate flat file (in the location which we specify in our pc). How can it be done? Hope your answers will be helpful for me to proceed further. Expecting for your reply...

With Regards

Sudhir S