Error Upload ckfinder + fckeditor

Make sure that you have defined all necessary resource types used by FCKeditor in config.php (located in ckfinder directory).
By default CKFinder comes with three resource types: Files, Images, Flash.

However, in FCKeditor default image upload path points to Image (without "s" at the end)

FCKConfig.ImageUploadURL = FCKConfig.BasePath + 'filemanager/connectors/' + _QuickUploadLanguage + '/upload.' + _QuickUploadExtension + '?Type=Image' ;

So the solution is to:
either change the name of resource type in config.php to "Image"
or
change Type=Image to Type=Images in a file, where you integrated FCKeditor with CKFinder (remember to clear your browsers cache if you modified javascript files).