WDS client unattended answer file not responding

I have installed Win2008 R2 on a Virtual Box and connected another virtual machine as client through internal network on Virtual Box. I created WDS Client Unattended answer file using WAIK saved it in Wdsclientunattended under RemoteInstall folder and enabled and located the answer file under client tab on WDS server properties. The problem is when i boot the client it prompts me for UI interfaces such as the first Language select, image select, partitions etc and looks like the unattend answer file is not responding at all. Any help would be appreciated !

Thank you