TADOQuery "specified type was invalid"

Hi

I am trying to write a blob to an interbase 5 database. I am using an
ODBC data source name and Delphi 5 enterprise update pack 1.
When I try to write a blob to the database ( see code below )I get the
following error : "A specified type was invalid".
What does it mean? However, when reading a blob from the database seems
to have no problems( e.g. myBitmap.Assign( FieldByName( 'Icon' ) ); )!
Any clarification greatly appreciated.
Paulo

procedure TForm1.Button1Click(Sender: TObject);
begin
  qryAddIcon.Parameters.ParamByName( 'IconName' ).Value := 'A Name';
  qryAddIcon.Parameters.ParamByName( 'Icon' ).Assign(
Image1.Picture.Bitmap );
  qryAddIcon.ExecSQL;
end;