Somebody had the same problem, and wrote this:
"Ok, the issue turned out to be a misconfiguration error in Plesk (my server control panel). Plesk was turning on php safemode and overriding the php.ini file. With the php safemode on, the install script was unable to move files from the extracted tmp install directories to the final destination directories."
And I looked in tmp folder there is k2, but I'm not sure, what am I suppose to do?
What is Plesk?