'This file type cannot be played' is always showing up

[Riley1234]

So I downloaded a TV series using uTorrent Web onto an external hard drive as my laptop does not have enough space. The download is all fine. I go out and close uTorrent and unplug the hard drive. Later, I plug the hard drive back in and open uTorrent Web and I go to press play on one of the episodes I had downloaded. 'This file type cannot be played' shows up and I do not know what I can do about it. But the file is still seeding, whatever that means. Please help