Hello,
If your string is UTF8 you musn't encode it again to UTF8, because PHP fails and recode it showing wrong characters.
Please avoid encoding to UTF8 and enable this option:
encode_to_UTF8
in config/phpdocxconfig.ini file.
If you still have the issue paste the most simple script you can do with that error; or send both files to contact[.at.]phpdocx.com.
Regards.