If the report size is too big, ie., PHP uses more than say 1000 POST variables or has run out of memory and error_reporting has been turned off, such a situation will arise. Try increasing the max php variables allowed and script processing time and memory used in the php.ini (max_input_vars, 1000)
The following links are explanatory:
http://stackoverflow.com/questions/9505192/php-post-limited-to-1000-variables
http://stackoverflow.com/questions/5064485/php-limit-in-post-variables
https://www.a2hosting.com/kb/developer-corner/php/using-php.ini-directives/php-max-input-vars-directive