Fatal error: Allowed memory size of…

Hi.
I use Download Attachments plugin in a large and quite heavy site with many downloads in posts and pages. It works well but it slows down the whole page significantly and sometimes – lately more often – it crashes down edited posts/sites with error (different numbers when dots):
Fatal error: Allowed memory size of ... bytes exhausted (tried to allocate ... bytes) in /wp-includes/meta.php on line ...
Any fix or help? The server’s memory is set above the alerts.
Cheers,
Krzysztof Rzepka, Przemyśl