Please download a program called "GSpot", available here: http://www.headbands.com/gspot/
This program will tell you all the important information about your audio files. Just drag and drop your audio files into the GSpot main window and let the program do the rest. In the case of your .wav files, the information you need to look at is in the right-side middle area of the window, namely the "Codec", "Bitrate" and "Fs" (sampling rate).
Pick one of your .wav files that doesn't work, and please tell us what GSpot says about it.