"File format not supported" randomly appears

Yesterday I ejected my microSDHC and loaded all of the MP3’s I wanted in the main Music folder.   I also did a CHKDSK /r /x from Windows (which reported no problems).    After that, everything was good.    BTW, before I was not only getting “file format not supported”, I was also getting “file not found”.    I’m running the latest firmware.    All of my files are MP3’s ripped from CD’s with Windows 7 at the highest bitrate it offered.