CKEditor 4 library is not detected by Wysiwyg module The Wysiwyg installation instructions tell me to 


  Extract the archive and copy its contents into a new folder in the following location:
  sites/all/libraries/ckeditor
  
  So the actual library can be found at:
  sites/all/libraries/ckeditor/ckeditor.js


These 2 conditions are met, however in the overview of editors, the CKEditor is now red. So it sees something is there, it's just not right.
What can be wrong? where should i be looking to troubleshoot?
The WYSIWYG module is not compatible with CKEditor 4, because CKEditor 4 uses double quotes " around it's version string, where CKEditor 3 used single quotes '. This breaks the version detection regex in the WYSIWYG module.

You could use CKEditor 3, like Bruno suggests, or you could patch the WYSIWYG module like described here https://drupal.org/comment/6790812#comment-6790812.

In editors/ckeditor.inc, replace line 81:

if (preg_match('@version:\'(?:CKEditor )?([\d\.]+)(?:.+revision:\'([\d]+))?@', $line, $version)) {


with:

if (preg_match('@version:[\"|\'](?:CKEditor )?([\d\.]+)(?:.+revision:[\"|\']([\d]+))?@', $line, $version)) {


If you're not bound to using the WYSIWYG module, you could also use the CKEditor module.