weird problem about Require Human Verification on Configured Actions

[REZA_JOON]

Hello dear friends
I have this weird problem when in my forum in Admin CP -> User groups -> User-group Manager -> Edit User group (Unregistered) -> Require Human Verification on Configured Actions
set the option to yes and save and it doesn't save to yes and image verification doesn't show in registration i,m sure this problem is not about the server because i have another web site on that server and it works fine

--------------- Added [DATE]1265360356[/DATE] at [TIME]1265360356[/TIME] ---------------

any solution?