Helping some people with issues of non working Hyper Cache installations, I descovered they are adding the line
in the wp-config.php file not in the right place. The line of code has to be added after the line
define (‘WPLANG’, ‘it_IT’);
not at the end of the file. If you read carefully the comments in wp-config.php you find at some point this statement:
/* That’s all, stop editing! Happy blogging. */
and that means you have not to add other code after this line.
Have a nice caching (release 2.5 is almost there with new interesting features).