Probably due to large overhead on the SilkPerformer machine.
Downloaded files are not written to the hard disk (not really viable for multiple users), but rather into RAM and then trashed when the download completes.
Just curious to know how. Did the file physically get downloaded on the machine? Because I was told that this action will crash a machine and the action of downloading can be seen by monitoring the packet flow during the test. So if there is a way can you please share it?