I've followed your instructions about SecurityAssist ("security_assist" folder missing) and now the above errors are fixed.
However, now I've a problem with the upload process.
These are the errors that I receive in the upload's window:
Warning: unlink(/Applications/MAMP/htdocs/website/assets/dms/.thumbs/./logo_itour.png): No such file or directory in /Applications/MAMP/htdocs/website/webassist/kcfinder/core/class/uploader.php on line 654
Deprecated: The each() function is deprecated. This message will be suppressed on further calls in /Applications/MAMP/htdocs/website/webassist/kcfinder/lib/class_image.php on line 119