Ive already set a default application (gmplayer using add under open with), thats the problem, even under open with i have gmplayer selected, if i double click it, it gives me an error:
The filename "something.wmv" indicates that this file is of type "Microsoft WMV video". The contents of the file indicate that the file is of type "Microsoft ASF video". If you open this file, the file might present a security risk to your system.
Do not open the file unless you created the file yourself, or received the file from a trusted source. To open the file, rename the file to the correct extension for "Microsoft ASF video", then open the file normally. Alternatively, use the Open With menu to choose a specific application for the file.