Most people here would recommend using VLC - (click on link) _ (choose nearest mirror site) as it has in-built codecs & is generally very reliable. Much more-so than WMP!!!

When you say you launched a file in red, which folder was it in? Press the Refresh button in the LW Library to see if it is still red after LW has reaccounted for the new files. Red generally means the file isn't being shared. But if it's in the incomplete section, then red can mean it's no longer being downlded. Another incomplete file of the same name is usually created instead. So perhaps you clicked upon the wrong one. Incomplete files in red can be a bit of an issue. To find out more, search the word red on the forum from about 6 mths to a year ago or later.

A video file will need to have at least a few % downlded before it can be previewed. Also, when you preview a file, it created a file called PREVIEW - filename in the incomplete folder. After downlding the file, these preview files should be deleted. Otherwise they take up unnecessary space. So make sure you didn't click on a previous preview file when you tried to preview the video.

You can preview a file from the downld window rather than the incomplete folder in the library window which should be successful. But at least previewing/launching directly from the incomplete folder will not create a preview file.