drupal is welcoming other user after login
Thanks a lot guys, I found the problem,,, the caching of the login block was set to 1, i just made it no-cache for this block



mysql> select * from blocks where module like '%ajax%';
+-----+---------------+-------+---------+--------+--------+-------------+--------+----------+------------+-------+--------+-------+
| bid | module        | delta | theme   | status | weight | region      | custom | throttle | visibility | pages | title  | cache |
+-----+---------------+-------+---------+--------+--------+-------------+--------+----------+------------+-------+--------+-------+
|  35 | ajax_register | 0     | sky     |      1 |    -40 | rightheader |      0 |        0 |          0 |       |  |     1 |
|  39 | ajax_register | 0     | garland |      0 |      0 |             |      0 |        0 |          0 |       |        |     1 |
+-----+---------------+-------+---------+--------+--------+-------------+--------+----------+------------+-------+--------+-------+
2 rows in set (0.00 sec)

mysql> update blocks set cache=-1 where bid=35;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> update blocks set cache=-1 where bid=39;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0