Notice: Undefined index: #ajax in ajax_form_callback() (line 391 of /var/www/html/includes/ajax.inc) I'm having an a field set as unlimited in the options in my custom content type, whenever I'm clicking on "Add another item" the page is only loading AJAX and I'm getting this message in error log :


  Notice: Undefined index: #ajax in ajax_form_callback() (line 391 of /var/www/html/includes/ajax.inc).


Note: Though I haven't saved/updated the product there is also a message in dblog that node has been updated. This issues was not their previously until I updated my drupal version from  7.22 to 7.32 using drush
Found the solution for this issue in my case was with the max_input_vars which was occurring on Windows machine.


Go to C:\xampp\php (the path where you have installed your WAMP or
XAMPP).
Open the php.ini, the configuration file located there.
Approx on line 475 there would be max_input_vars = 1000 change that as per your need. In my case 1500 worked for me.


Note: I'm not sure increasing max_input_vars is a good practice, I have done that as I was having more than 10K fields in a single form. Still for those who are looking for an alternate solution in their development phase can opt this solution for time being.