Which sound recorder were you using? I've tested a couple of different sound recorders, including Samsung's. In renaming the file, I found no instance of it not being able to be played back. Can you go through the steps you did to name the recording? When I went to save the recording and I was asked what I wanted to save it as, there was no date in the name field - only what's shown on the image. This was true regardless which recorder I used, so changing the name should do nothing to make the recording unplayable. Have you gone into the file manager and located the recording? If you used Samsung's recorder, it should be in a folder called voice recordings. Make sure it shows the extension of m4a or mp3. If the extension is missing, it will not play. If it is missing, just edit the file name in the file manager and add the .m4a extension. It could also be that the recording somehow got corrupted.
