[Difficulty in simulating following Buck Converter PSpice listing]

actually i am getting error message
                      ERROR -- Less than 2 connections at node O
while simulating this code

*Buck Converter

*PWM
VRAMP 1 0 PULSE (1 4 0 398U 1U 1U 1U 400U)
R1   1 0 1K; dummy load
VREF    5 0 DC 12
R1   5 0 1K; dummy load

*Amplifier
E1 7 0 8 5 30

*Power Circuit
VI 2 0 DC 15
SI 2 3 1 7 SWITCH; includes comparator
DS1 3 2 DIODE
D1 0 3 DIODE
L 3 8 20M
C 8 0 47U
RL 8 0 22

.MODEL SWITCH VSWITCH(VON = 0.01 VOFF = -0.01 RON  = 0.1 ROFF = 100K)
.MODEL DIODE D
.OPTIONS ITL4=20 ITL5=0 LIMPTS=0 RELTOL=0.01
.PROBE V(1) V(3) V(8) V(7) I(L)
.TRAN 50U 25M 0 50U
.END

[simulating circuits with ICs in orcad]

while simulating this in Pspice A/D i get above. please help me.

*Buck Converter

*PWM
VRAMP 1 0 PULSE (1 4 0 398U 1U 1U 1U 400U)
R1   1 0 1K; dummy load
VREF    5 0 DC 12
R1   5 0 1K; dummy load

*Amplifier
E1 7 0 8 5 30

*Power Circuit
VI 2 0 DC 15
SI 2 3 1 7 SWITCH; includes comparator
DS1 3 2 DIODE
D1 0 3 DIODE
L 3 8 20M
C 8 0 47U
RL 8 0 22

.MODEL SWITCH VSWITCH(VON = 0.01 VOFF = -0.01 RON  = 0.1 ROFF = 100K)
.MODEL DIODE D
.OPTIONS ITL4=20 ITL5=0 LIMPTS=0 RELTOL=0.01
.PROBE V(1) V(3) V(8) V(7) I(L)
.TRAN 50U 25M 0 50U
.END