There is a maximum path length (about 30 chars) for the full path name to the .WAV file. This happens when the character limit of the path is exceeded. Its not too hard to exceed, for example:

C:\Documents and Settings\username\My Documents\sounds\sound-name23.wav

All problems will usually go away if you use Windows Explorer to create a folder in the Ensign directory called Waves and copy the wave files to it.

C:\Ensign\Waves\sound-name23.wav

Then use the browse button on the alert form to find the file in the new Waves folder to play.