Raise application error

I have a question.

In a PL/SQL procedure I used on Oracle 11G raise_application_error like this:

IF (SmaakId = -1) THEN

        raise_application_error(-20995, 'De Smaak met SapNr "'||TO_CHAR(SapSmaakNr)||'" bestaat niet in de database');

    END IF;

It works perfectly.

But on Oracle 12c I get this back:

(Error : DataAccess.Artikelen.AddSapArtikel() failed with error 'ORA-20995: Message 20995 not found; product=RDBMS; facility=ORA-20995: Message 20995 not found;  product=RDBMS; facility=ORA')

I tried it also in a EXCEPTION Block, with the same result.

What is wrong?