rugarch xts causes error

Hi
Used example provided by Alexios in some thread
===========================
library(rugarch)
library(xts)
data(sp500ret)
spx<-xts(sp500ret, as.Date(rownames(sp500ret)))
xreg<-xts(rnorm(nrow(spx)), index(spx))
colnames(xreg)<-"xreg"
# assume xreg is an actual series, so we lag it
# as we would do in a real application
xreg = lag(xreg,1)
inputs<-na.omit(cbind(spx, xreg, join="left"))
# real time forecasting
spec<-ugarchspec(mean.model=list(external.regressors=inputs[1:2000,2]))
fit<-ugarchfit(spec, inputs[1:2000,1])
# 2 ways to do real-time forecasting (ugarchforecast and ugarchfilter)
# Example: forecast points 2001:2020
xforc = xts(matrix(NA, ncol=2, nrow=20), index(inputs[2001:2020]))
sforc = xts(matrix(NA, ncol=2, nrow=20), index(inputs[2001:2020]))
for(i in 1:20){
 ? # Forecast(T+1)|Information(T)
 ? # 1. Create a similar spec as you used in estimation
 ? # and add the lagged regressor upto time T
   
specf1<-ugarchspec(mean.model=list(external.regressors=inputs[1:(2000+i-1),2])) 

 ? # Pass the estimated coefficients from the estimation upto time 2000
 ? setfixed(specf1)<-as.list(coef(fit))
 ? # 2. Forecast using ugarchforecast on a specification with fixed 
parameters
 ? # where n.old is used in order to recreate the correct start-up 
conditions
 ? # used in the fitting routine
 ? f1<-ugarchforecast(specf1, inputs[1:(2000+i-1),1], n.ahead=1, 
n.old=2000)
 ? # 3. Forecast using ugarchfilter on a specification with fixed 
parameters.
 ? # For this method, append a new row to the end of the data with zeros,
 ? # as you would do with related filters. This forces the routine to
 ? # output the value at time T+1
 ? newdat<-rbind(inputs[1:(2000+i-1),],xts(matrix(0, nrow=1, ncol=2),
                                           
tail(move(index(inputs[1:(2000+i-1)])),1)))
 ? specf2<-ugarchspec(mean.model=list(external.regressors=newdat[,2]))
 ? setfixed(specf2)<-as.list(coef(fit))
 ? f2<-ugarchfilter(specf2, newdat[,1], n.old=2000)
 ? # fitted = estimated conditional mean values for uGARCHfit objects
 ? # fitted = forecast/filtered conditional mean values for 
uGARCHforecast/uGARCHfilter objects
 ? xforc[i,1] = as.numeric(fitted(f1))
 ? xforc[i,2] = as.numeric(tail(fitted(f2),1))
 ? # sigma = conditional sigma values (fitted/forecast etc)
 ? sforc[i,1] = as.numeric(sigma(f1))
 ? sforc[i,2] = as.numeric(tail(sigma(f2),1))
}
# check
all.equal(xforc[,1], xforc[,2])
all.equal(sforc[,1], sforc[,2])
# check that the 1-ahead forecast directly from the fitted object is also
# the same
all.equal(as.numeric(xforc[1,1]), as.numeric(fitted(ugarchforecast(fit,
                                                                   
 ?n.ahead=1))))
all.equal(as.numeric(sforc[1,1]), as.numeric(sigma(ugarchforecast(fit,
                                                                   
n.ahead=1))))
# check the filter values vs the fitted values (i.e. why we use the 
n.old argument)
all.equal(fitted(fit), fitted(f2)[1:2000])
all.equal(sigma(fit), sigma(f2)[1:2000])
==========================
But, when running it i get an error:

 > fit<-ugarchfit(spec, inputs[1:2000,1])

Error in pars[idx["mxreg", 1]:idx["mxreg", 2], 1] <- fit.mean[i] :
 ? replacement has length zero