No permission for direct access to security database
This message shows up when you try to change password on Firebird 2.0 database using some of older methods that access the database file directly. Firebird 2.0 prevents this, as it is a security issue. The only way to update passwords is via Services API. Use the appropriate interface your connection library provides.
Alternatively, you can use Firebird's gsec tool:
gsec -database path -mo username -pw new_password -user sysdba -pass masterkey
For example, to change SYSDBA password from masterkey to mykey:
/opt/firebird/bin/gsec -database localhost:/opt/firebird/security.fdb -mo sysdba -pw mykey -user sysdba -pass masterkey