I have installed apache's MPM and disk cache modules, XCache for PHP, and w3 total cache plugin to spped up my WPMU installation.
Overall the website seems to do just fine, but when I visit /wp-admin/ pages, often the response time insreases considerably, and getting sometimes 404 insted of requested page, or "Fatal error: Allowed memory size of ... bytes exhausted".
XCache seems to work fine and memory_limit is set to 64MB. Where should I dig to solve the problem?
