When upgrading from an older version to 3.0.5 all files where supposed to be moved from the installation folder to Documents\Sokoban 3. The code that moved the sound files moved all files ending with .wav, but missed Yahoo.Wav because of the capital W.

Fix this by downloading here:
http://www.sourcecode.se/sokoban/download/Yahoo.Wav
save it in the MyDocuments\Sokoban 3 or Documents\Sokoban 3 folder, depending on Windows version.

Björn