Unable to add menu items from backend

I have a serious problem: I cannot add menu items to the Main Menu by backend. Description of the problem:
If I go to Menu-->Main Menu--> click the green button New -->click the blue button select it appears the drop list with Articles, Configuration manager,.... but when I select an entry it does not appear on the field "Menu Item Type". "Menu Item Type" remains empty.
If I did not explained well myself please here you can find the video:
http://youtu.be/9fqmUxb8Jho
It is not a server problem cause I have another joomla website where the droplist works.
It is not a browser problem cause I tried with firefox chrome and internet explorer and I am always unable to populate the gray field menu item type.
Joomla version is 3.3.6 and I did not installed anything: no plugin, no extensions,.... I cleared cache many times.

My website is casino-online.bz user: gavick password: gavick
Can I send you the admin backend password to someone of you to look inside?

Hello,

Please try to do following:

in the index.php file of the Isis back-end template please change:

Code: Select all

// Add JavaScript Frameworks
JHtml::_('bootstrap.framework');

to:

Code: Select all

// Add JavaScript Frameworks
JHtml::_('bootstrap.framework');
JHtml::_('behavior.framework', true);

Done, but the problem still occurs.
I updated /administrator/templates/isis/index.php with your code.

Cleared cache, logged out and in, rebuilt the menu .... but nothing.

Could this be the problem?
[24-Oct-2014 15:52:40 Europe/Berlin] PHP Warning: base64_decode() has been disabled for security reasons in /home/casinoon/public_html/administrator/components/com_menus/controllers/item.php on line 349

found many on error log of administrator directory, they seems raised everytime I try to add a menu item.

I enabled base64_decode() and now everything works.