If you see something like this on your WordPress installation,
Deprecated: Function create_function() is deprecated in /home/$username/public_html/wp-content/plugins/revslider/includes/framework/functions-wordpress.class.php on line 258
Warning: Cannot modify header information - headers already sent by (output started at /home/$username/public_html/wp-content/plugins/revslider/includes/framework/functions-wordpress.class.php:258) in /home/$username/public_html/wp-content/plugins/qtranslate-x/qtranslate_core.php on line 388
Warning: Cannot modify header information - headers already sent by (output started at /home/$username/public_html/wp-content/plugins/revslider/includes/framework/functions-wordpress.class.php:258) in /home/$username/public_html/wp-includes/pluggable.php on line 1251
Warning: Cannot modify header information - headers already sent by (output started at /home/$username/public_html/wp-content/plugins/revslider/includes/framework/functions-wordpress.class.php:258) in /home/$username/public_html/wp-includes/pluggable.php on line 1254
it means that there is something wrong with your WordPress file(s).
There are two files mentioned by the error.
The first file (in our case: my-function.php located at /public_html//wp-content/plugins/revslider/) is the chief culprit of the error which may have been used to override the core functionality provided by WordPress.
The core functionality in question is in the pluggable.php file (a core WordPress file which is the same for every WordPress installation).
There is a problem in the first file which is preventing the second file to function properly.
Often this is caused by blank spaces present in the first file.
Using a text editor, you may want to remove the empty line at the end of your script (after the final "?>" or "php>" string) or preferably **re-install the plugin**
If a core WordPress file is the culprit of the error, your best option would be to download WordPress and get yourself a clean copy of the WordPress file.
Then replace the corrupted file on your installation with the one present on the clean version.
