firebird-mirror/src/misc/upgrade/v2/security_database.txt

  You can't use pre-2.0 security database in firebird 2.0 or higher directly.
  If you try to put old security.fdb into firebird's new home directory with 
new (security2.fdb) name, you will get a message - cannot attach to password 
database. That's OK and is by design. In order to be able to use old database, 
you must run appropriate upgrade script - security_database.sql. To do so:
  1. Put your old security database in some known to you place (not new home
directory). Always have a copy of it!
  2. Start firebird using it's new, native security2.fdb.
  3. Convert your old security database to ODS11 (i.e. backup and restore it 
using gbak from firebird 2.0). Without this step you will get failure running 
security_database.sql!
  4. Connect to restored database as SYSDBA and run the script.
  5. Stop firebird.
  6. Copy upgraded database to firebird's home directory (as security2.fdb).
  7. Start firebird.

  Now you should be able to connect to firebird 2.0 server using your old 
logins and passwords.