Removing sound files??

How do you remove imported sound files?
The error console keeps displaying the following message:
Alice version: 2.2 8/1/2009

Your sound file cannot be played in Alice.
Please find an audio editor to convert the file to one with a PCM encoding.
See the tutorial on converting sound files at our Alice website.
Right click to clear the messages here.

Unable to handle format: mpeglayer3, 11025.0 Hz, 16-bit, Mono, LittleEndian, Signed, 2500.0 frame rate, FrameSize=8 bits

Failed to realize: com.sun.media.PlaybackEngine@1c77f54

Error: Unable to realize com.sun.media.PlaybackEngine@1c77f54[/I][/I]


I have edited the sound file then changed it with one that I know is good. I cleared the error console as well. But everytime I open the file, I see the error dialog.