Erro no banco Firebird 1.5

estou criando a seguinte procedure
DELETE FROM contratos C
WHERE C.data_atu < ´1/31/2002´;
ai me aparece esta mensagem de erro. O que pode ser?

Error Message
Unsuccessful execution caused by a system error that precludes
successful execution of subsequent statements.
internal gds software consistency check (can´t continue after bugcheck).


SQL TEXT
select RDB$RELATION_NAME from RDB$RELATIONS
where (RDB$RELATION_NAME = ´CONTRATOS´) and
(RDB$VIEW_SOURCE is NULL)