Why Does LTspice Report Unknown Subcircuit for a 1N5231B Zener Diode?

[xcvxcvvc]

* C:\Documents and Settings\****(myusername)\Desktop\project\projectSimulation.asc
Vin Vin N001 SINE(0 22.2 60)
C1 Vc 0 100e-6
XDz 0 Vout 1N5231B
RLIMIT Vc Vout 10
RLOAD Vout 0 500
D1 0 Vin 1n4004
D2 Vin Vc 1n4004
D3 N001 Vc 1n4004
D4 0 N001 1n4004

.lib C:\Program Files\LTC\LTspiceIV\lib\cmp\standard.dio
.lib C:\Documents and Settings\<username>\Desktop\project\1n4004.mod
.lib C:\Documents and Settings\<username>\Desktop\project\1N5231B.lib
.tran 0 1 0 .1m
.backanno
.end

The above is my code. My .lib statement correctly imports and uses the 1n4004 diode I found. However, the subcircuit representing my 1N5231B Zener keeps giving me this error:
Fatal Error: Unknown subcircuit called in:
xdz 0 vout 1n5231bHere are the contents of the 1N5231B.lib:
***************** Zener Diode Electrical Parameters ******************
** Product: 1N5231B
** Package: DO-35 Glass Case
**--------------------------------------------------------------------
* Node: anode cathode
.SUBCKT F1N5231B 2 1
D1 2 1 MD1
.MODEL MD1 D IS=2.14005e-10 N=2.0 XTI=1 RS=0.656
+ CJO=1.5e-11 TT=1e-08
R 1 2 MDR 4.00e5
.MODEL MDR RES TC1=0 TC2=0
RZ 2 3 10.8
IZG 4 3 0.1
R4 4 3 10
D3 3 4 MD3
.MODEL MD3 D IS=2.5e-12 N=1 XTI=0 EG=0.1
D2 5 4 MD2
.MODEL MD2 D IS=2.5e-12 N=3 XTI=0 EG=0.1
EV1 1 5 6 0 1
IBV 0 6 2.0e-02
RBV 6 0 MDRBV 185.5
.MODEL MDRBV RES TC1=1.0e-7
.ENDS
**********************************************************************
** Creation: Mar.-17-2009 Rev: 0.0
** Fairchild Semiconductor