|Project:||CKEditor - WYSIWYG HTML editor|
If svn isn't installed, you get a pretty generic error:
Drush was unable to download CKEditor to /var/www/sites/all/libraries/ckeditor.
First thought to fix was permisssions, after all how often does installing subversion solve the problem? :P
The devel patch above shows the failed exec line which would help in debugging.