Generating File Preview with Nitro

Just got my atv take 2 working on my apple tv. I have an external USB hard drive attached to the apple tv. I have imported a few home movies which play fine but I cannot get generation of a preview image of the video to show what it is. If I import the same movie into AppleTV directly, a preview picture of the movie is generated. On one of the nito tv boards, is says to hold the left arrow key to regenerate a new preview, but that doesn’t work for me.

Any advise appreciated.

Thanks in advance