blank page or sql error when deleting large amount of posts - spam in forum.
That error happend because you have exceeded memory limit in php.
so you need to setup much higher limit in php.ini for
; Maximum amount of memory a script may consume (128MB)
; http://www.php.net/manual/en/ini.core.p ... mory-limit
memory_limit = 1024M
But you need to do that before you delete those spammers and their spams, to properly delete them.
If not, delete database and than restore it and delete user again after rising memory limit.