If you’re utilizing memory intensive modules which requires the php to access more memory than standard installations, change the value in the php.ini file (some hosts require system administrators to make this change).

For your local MAMP setup edit this file:
/Applications/MAMP/conf/php5/php.ini

Look for the following line and change accordingly…

memory_limit = 96M ; Maximum amount of memory a script may consume (8MB)

For Drupal installation you may change…

You may edit the root .htaccess:

# Override PHP settings. More in sites/default/settings.php
# but the following cannot be changed at runtime.

and immediately after this add the following line:

php_value memory_limit 96M

You may also edit the settings.php…
Locate the PHP settings section and add the following line at the end of that section:

ini_set(‘memory_limit’, ’96M’);

>> Make sure you use Capital M <<

Everything is explained in http://drupal.org/node/207036