Sounds will not play when not set to default ones

When I change a few system event sounds, such as Logon and Logoff soundswith two particular files, NOT default Windows sounds, and "test" they won't play, but if I set them back to default or any other .wav file in the drop-down list, those all work. I might note, that I made this change and did have the sounds working, but now, they won't work at all. I have tried to move the file and redirect the "system" to the new location and nothing. I can open the sound clips in Media Player and they are fine, but "windows" just won't play the audio when I logoff or logon. Any suggestions folks?