Same problem here
Blank Page on K2 Items in Backend (latest joomla 2.5 with latest k2)
temporary the problem solved if i logout and login back to joomla or if i empty cache and cookies from browser. but returns after few minutes
Server error log (latest PLESK):mod_fcgid: stderr: PHP Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 3898 bytes) in /var/www/vhosts/develsites/httpdocs/libraries/joomla/database/database/mysqli.php on line 498, referer: http://........./administrator/index.php (every time i reload this blank page i got the same error)
same problem with 256Mb or more in php
Dedicated server with 32Gb Ram with centos & Plesk (the 2 other of my sites works perfect in joomla without k2 and wordpress with extremly low cpu utilization)
I tested the site with several server configuration on local machines (xampp, lampp, mampp, plesk,cpanel, centos debian windows) and various host providers WITH THE SAME RESOLTS. I also notice extreme high cpu usage on k2 items (on frontend) with only few users