This error is nothing new, per se, as far as I know it was present also in previous versions of wordpress (I’m a fresh new user and I’ve been using v3+ for more than I’ve been with 2.9.7 (first one I installed).
When this error occurred in previous versions, all you needed to do was open the [WORDPRESS FOLDER] > wp-settings.php file, and change the maximum allowed allocable ram from there. And that’s what most guides still tell you to do now, leaving you stranded as that line you need to change is not there anymore.
What you see though, is that at the beginning of the wp-settings.php file there is a line that says:

require( ABSPATH . WPINC . '/default-constants.php' );

which pretty much says it all, unless you are not the least bit PHP savvy (hence, this guide is for you).
All you need to do is open the [WORDPRESS FOLDER] > wp-includes > default-constants.php file, and change the line:

define('WP_MEMORY_LIMIT', '32M');

into

define('WP_MEMORY_LIMIT', '40M');

or anything of your liking (may be 36M, 48M, or whatever depending on your setup); obviously, the lower the better for the performance of your server, especially if you’re on a shared hosting.

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