UI slows and window elements won't display after screensaver path changed and it is invalid

I have been transferring my video library to the USB drive attached to my Boxee Box after reformatting it to ext4.

Each time I've copied around 200GB of data to the USB drive over the network and somewhere during the transfer the Boxee Box UI will start going very slow and the drop down top menu element won't display. If I arrow left or right on the home screen I hear the button press audio immediately but then it takes a few seconds for the highlighted object to shift.

Pressing the menu/back button on the remote fails to show the top menu, though I can then arrow left and right and I hear button presses but none of the home screen UI elements change as if I am moving around on a hidden top menu.

If I try to play a video from the file browser I hear the selection sound but the playback options screen does not display. The UI then responds to up/down presses as if the playback option screen was not presented, (it moves up and down to the files around).

This renders the Box pretty useless until it is power cycled. The SMB transfer continues while the box is in this state.