More information...I tried to open the converted mp3 files in Sound Studio 3.5. They appear to load, that is the window has the file name in at the top, but there is no visible audio waveform as expected and of course they will not play. Sound Studio does not open wma files at all, I believe. Also in iTunes, the converted mp3 files show a size that is about 1/10th of the average working files, and their "Time" is zero.
When I converted in Switch Plus, I also checked Normalize assuming they would be serial processes. It looked as if it was normalizing the file, taking a few seconds and appeared to be processing data. I tried turning off Normalization and now the wma to mp3 conversions work in iTunes.
Go figure...probably a rookie issue. Thanks for your help.