At 11:11 AM 1/06/2009, you wrote:

>I use FB 2.1.2, following message's shown when I exectute a procedure:
>
>Unsuccessfull execution caused by a system error that precludes successful
>execution of subsequent statements.
>Internal gds software consistency check(cannot restore singleton select
>data(284), file: rse.cpp line: 3426).

It's a bug:
http://tracker.firebirdsql.org/browse/CORE-2291

It is fixed in the forthcoming v.2.1.3, but you can download a snapshot if you don't want to wait.

./heLen