[Snippet] MaxiGallery - Copy&Paste error

Hello,
after loggin in with admin account
I tried to use MaxiGallery snippet (0.4.1) but when I save the copy-pasted
MaxiGallery code in the snippet textarea I obtain this error message:

Forbidden
You don’t have permission to access /modx/manager/index.php on this server.

I have to paste the code in mySQL directly.

This happens only with the MaxiGallery code
because I have a lot of snippet in the manager
that works fine

Your server provider has some restriction on certain string what cannot be in POST data. You can see what it is by copy pasting the code in smaller chunks at a time and see where that error pops up.