For more information on resolving this issue with your code, please refer to: http://www.php.net/manual/en/language.references.pass.php

[Not recommended]
However, to prevent this warnings from displaying, add "~E_STRICT" to your php.ini on the error_reporting line. Such as:
error_reporting = E_ALL ~E_STRICT

> it was perfectly worked on php 5.3.10, but after upgrade php version it will not working.

The reason you are seeing this message after upgrading, is that strict warnings (E_STRICT) became part of E_ALL in 5.4.0. The default value for `error_reporting` in 5.5.7 excludes E_STRICT, however if you didn't alter your php.ini file, you will still have the 5.3 default which doesn't exclude E_STRICT:

5.3: # Default Value: E_ALL & ~E_NOTICE

5.5: # Default Value: E_ALL & ~E_NOTICE & ~E_STRICT & ~E_DEPRECATED

The correct action to resolve this is to add `& ~E_STRICT` to your existing error_reporting value in php.ini.

http://php.net/manual/en/function.error-reporting.php#refsect1-function.error-reporting-changelog

the problem you are having is that you are passing the return of the function call "_block_get_renderable_array" to drupal_render. drupal_render expects that parameter to be passed by reference. You can only pass a variable by reference NOT the return value of a function call. Here is an example fix.

$block = block_load('block', '7');
$render_block = _block_get_renderable_array(_block_render_blocks(array($block)))
$output = drupal_render($render_block);
print $output;