Cannot enter to ACP after convert DB from 3.0.12

After full convert DB from 3.0.12 cannot enter to Admin Panel, HTTP 500 Internal Server Error.
Here is the log of PHP:

PHP Fatal error: Uncaught exception 'Exception' with message 'DateTime::__construct(): Failed to parse time string (@) at position 0 (@): Unexpected character' in C:\Inetpub\phpBB3.asc\phpbb\datetime.php:50
Stack trace:
#0 C:\Inetpub\phpBB3.asc\phpbb\datetime.php(50): DateTime->__construct('@', Object(DateTimeZone))
#1 C:\Inetpub\phpBB3.asc\phpbb\user.php(713): phpbb\datetime->__construct(Object(phpbb\user), '@', Object(DateTimeZone))
#2 C:\Inetpub\phpBB3.asc\includes\acp\acp_main.php(586): phpbb\user->format_date(NULL)
#3 C:\Inetpub\phpBB3.asc\includes\functions_module.php(652): acp_main->main('main', 'main')
#4 C:\Inetpub\phpBB3.asc\adm\index.php(81): p_master->load_active()
#5

thrown in C:\Inetpub\phpBB3.asc\phpbb\datetime.php on line 50