I’ve just updated my WordPress to version 3.2, when update has been finished a page with error code 500 was displayed. In log file had many entry of Fatal error: Allowed memory size of 33554432 bytes exhausted
To know if it your problem too, edit file error_log in wp-admin directory and and take a look at last rows.
The following process fixed this for me, but your host server should allow sizing PHP memory at runtime.
Open and edit file wp-settings.php at root of WordPress directory and put the row bellow after “<?php”:
define('WP_MEMORY_LIMIT', '64M');
Here I’ve set up to 64MB to PHP, but how to know amount of MB to set up?
In error message, the long number means amount of bytes allocated to PHP: “Fatal error: Allowed memory size of 33554432…”. This number represents 32MB (do this calculation to converts byte in megabytes 33554432 / (1024^2) = 32).
Just set a number greater than the result in line above.

