This problem was solve.

I install fresh elgg on serverB and got any problem.

I see settings.php that elgg generated. And I found something weird looks like this

$CONFIG->dbuser = ''db_username'';

There is double single-quote around db_username.

Then I compare php.ini file for serverA with serverB. I see something difference.

serverA

; Magic quotes for runtime-generated data, e.g. data from SQL, from exec(), etc.
magic_quotes_runtime = Off

; Use Sybase-style magic quotes (escape ' with '' instead of \').
magic_quotes_sybase = Off

serverB

; Magic quotes for runtime-generated data, e.g. data from SQL, from exec(), etc.
magic_quotes_runtime = On

; Use Sybase-style magic quotes (escape ' with '' instead of \').
magic_quotes_sybase = On

Then I change magic_quotes_runtime =Off and magic_quotes_sybase =Off in php.ini file on serverB.

It works. I can install fresh elgg. And my elgg that I move for serverA to serverB work too.

If somebody have any idea, please share.

Thank you.