Inserting Block with Custom Input Filter Module via Shortcode Causing http 500 error I have a custom input filter module, and I am trying to figure out why it crashes when I attempt to insert a block into a post via a shortcode. The method works perfectly when I am inserting a string, but when I try to insert a block, it causes a http 500 error. 

Any ideas? I am using Drupal 7.15. Also, I have tried the insert_block module, and it generates a similar error...

Here is the input filter process that works (with a string)

function _related_links_filter_related_block_process($text, $filter, $format) {
   $shortcode_regexp  = "/\[block\]/";
   $output = "Text string inserted in via shortcode";

   return preg_replace($shortcode_regexp, $output,$text);
}


Here is the input filter process that causes the error (with a block)

function _related_links_filter_related_block_process($text, $filter, $format) {
   $shortcode_regexp  = "/\[block\]/";
   $block = block_load('block', 3);
   $output = drupal_render(_block_get_renderable_array(_block_render_blocks(array($block))));

   return preg_replace($shortcode_regexp, $output,$text);
}


Any help is appreciated!
A 500 error can be caused by lots of things. Your best bet is probably to use the Watchdog and/or Apache logs to narrow down the specific cause(s).