J3.x:Validation error on creating a menu entry
From Joomla! Documentation
This pertains only to Joomla! version(s): 3.4.2
What is the cause
You can't add the new entry to the menu.
How to fix
Apply the patch https://github.com/joomla/joomla-cms/pull/7317.
This will be included in Joomla 3.4.3