Background job and open dataset

Hi friends

I am running a report for writng the output to the application server with open dataset

When I run it on line , every thing seems to be ok and the file is created nicely , but nothing happens when I run the report in background job , the job is excuted with success but the file is never created, I have the autorasition for writing and reading in the sap directory.

what can be the problem.....?