If a file is colored red it usually means that someone else is uploading the file from you or that it is being accessed by another program like Mediaplayer or another media player type application.
If neither of these situations are happening it sounds like you may have accidentally downloaded a virus infected file in which case you had better do a thorough scan of all your recently downloaded files with a good quality Antivirus application. If you can't find anything there, you will need to come back and post a new post in these forums giving as much information as you can about your system and the versions of LimeWire that you are using.
Another good thing to do is to read as many of the "Sticky" threads at the beginning of these forums as you possibly can. Quite often the moderators have seen a problem before and post these sticky files in order to alert as many people as possible to a solution as possible.
Good Luck!