Error by adding an exclamation mark !

[Piotr]

> I'm not top posting.

\version "2.16.2"
%{
A reminder accidental can be forced by adding
an exclamation mark ! after the pitch.
Here it makes error.
%}

\relative c''   {
                        \clef "treble" \key bes \major \time 6/8
  \autoBeamOff b8 a es!'~ es16[ c] d[ g] e8~|
}