It looks like you have lost a line break in your configure file:
If the window is the right width, the define('DIR_WS_ADMIN', '/admin/'); statement appears on its own line, but if the window is wide enough or narrow enough (or in PHP code highlighting mode), you will see that there is only a space between
// * DIR_WS_* = Webserver directories (virtual/URL)
// these paths are relative to top of your webspace ... (ie: under the public_html or httpdocs folder) define('DIR_WS_ADMIN', '/admin/');
meaning that that statement is part of the comment above it and not being defined.