It seems like the order of the parameter is important even if I use
named parameters like this:

_cmdMove = DatabaseHelper.GetCommand("ADDREPERTOIREMOVE");
_cmdMove.CommandType = CommandType.StoredProcedure;
_cmdMove.Parameters.Add("@REPERTOIREMOVEGUID", FbDbType.Guid);
_cmdMove.Parameters.Add("@REPERTOIREPOSITIONBEFOREGUID", FbDbType.
Guid);

...

My stored procedure:

CREATE PROCEDURE ADDREPERTOIREMOVE (
REPERTOIREMOVEGUID CHAR(16) CHARACTER SET OCTETS,
REPERTOIREPOSITIONBEFOREGUID CHAR(16) CHARACTER SET OCTETS,
REPERTOIREPOSITIONAFTERGUID CHAR(16) CHARACTER SET OCTETS,
REPERTOIREGUID CHAR(16) CHARACTER SET OCTETS,

....

This surprised me. I would expect that I could add these parameters in
any order as I'm using variable names, but when I change the order of
adding the parameters the first parameter is always matched to
REPERTOIREMOVEGUID, the 2nd to REPERTOIREPOSITIONBEFOREGUID etc. no
matter what the name of the parameter is.

So basically the names have no real impact except that they give me
some kind of oriantation and of course if I change the values for
executing the same procedure more than one time I can easier match the
values to the parameters.

Anyway, I think this is an easy way to go wrong and I wonder if a
future Firebird version is going to change this?

Beside that I'm deeply impressed by Firebird. I have spent quite some
time with it now and I can't believe how professional this database is
in all meanings and yet for free.

Stefan