I had the same problem and finally figured out what it was...so here is all the information...

My MySQL charset: UTF-8 Unicode (utf8)

so I had to change 2 lines in 2 files and it works perfectly now.

/includes/languages/english.php
/admin/includes/languages/english.php

look for
setlocale(LC_TIME, 'en_US.ISO_8859-1');

and change it to
setlocale(LC_TIME, 'en_US.utf8');

then look for
define('CHARSET', 'iso-8859-1');

and change it to
define('CHARSET', 'uft-8');

Do this in both files, and those error characters will not show up any more. :-)

I hope this helps someone!!!