I got an error "Failure while aqcuiring locks" when I trying to install phpBB 3.3.0.
My host's service desk fixed the problem and I got a phpBB installed.

He said that problem was:

• release() function doesn't remove .lock file > trying to open the file in read mode and locks it
• "It also means that in order to place an exclusive lock, the file must be opened for writing" http://man7.org/linux/man-pages/man2/flock.2.html
• added line between lines 140 and 141 "unlink($this->path . '.lock');" to flock.php
  https://github.com/phpbb/phpbb-app/blob/master/phpbb/lock/flock.php