SELECT username_clean FROM phpbb_userconv GROUP BY username_clean HAVING COUNT(user_id) > 1
in file /var/www/vhosts/serbian-fm.net/httpdocs/phpBB3/phpbb/db/driver/driver.php on line 999
BACKTRACE
FILE: (not given by php)
LINE: (not given by php)
CALL: installer_msg_handler()
I don't know how this works but the error is saying that the table forum_phpbb3.phpbb_userconv does not exist. Either you have to manually create it, the conversion script should create and isn't doing so or the data that you are providing for the conversion is incorrect.
You would probably be better off asking the creator of the conversion script.
David Remember: You only know what you know and - you don't know what you don't know!
I now no longer support any of my extensions but they will start to become available here