Well, actually I found your solution after HOURS (or days, counting sleep time and working on something not depressing to restore my faith in forums) before I fixed my solution, so I was already saved… and also I'm writting you for the same reasons everybody writes you: to complaint, hehe. But I started saying it works! with my star :)
Now, the error is Warning: Invalid argument supplied for foreach() in /var/www/BLAHBLAH/wp-content/plugins/custom-menu-images/custom-menu-images.php on line 150 Warning: Invalid argument supplied for foreach() in /var/www/BLAHBLAH/wp-content/plugins/custom-menu-images/custom-menu-images.php on line 150
And I'd like to mention that if you upload the image in the same process (changing from Library tab to upload from computer) the button show there is "insert into post".
I don't know whether it's just the name of the button, or the image will be put as content of the DB entry…
Anyway, it's probably a small error.
Good work ocho manos! (se habla español, se habla) (con tono gaucho argentino)