Version 1.5 problems

Hello ,

Im getting error message in approve new user Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 71 bytes) in /public_html/site.com/wp-includes/wp-db.php on line 1551
and also im unable to search user in my site dashboard when new user approve plugin is activated..

please assist me how to solve this problem

http://ww.wp.xz.cn/plugins/new-user-approve/