  It is shown in this paper that the symplectic form for the system consisting
of $D$-dimensional bulk Palatini gravity and SO$(1,1)$ BF theory on an isolated
horizon as a boundary just contains the bulk term. An alternative quantization
procedure for the boundary BF theory is presented. The area entropy is
determined by the degree of freedom of the bulk spin network states which
satisfy a suitable boundary condition. The gauge-fixing condition in the
approach and the advantages of the approach are also discussed.
