R help - Jan 2004 - 'subscript out of bounds'

I have been having some trouble with a certain function and getting the message
''subscript out of bounds''.  The problem is that in the below
function, the first entry is not defined b/c it is singular and the tstat cannot
be calculated (it is defined as ''NA'').  R though will not put
an ''NA'' in tstat[1,1] as I would like it to.  Is there any way
I can make this happen and therefore allow R to calculate the next entry in
tstat?
 
 
Yi<-c(23,54,67,34,56,78)
x1<-c(1,1,1,1,1,1)
x2<-c(1,0,1,1,0,0)
x<-rbind(x1,x2)
kn<-2 #number of rows in x
 tstat<-matrix(0,kn,1)
          
          for (k in 1:kn){
          lm1<-lm(Yi~x[k,])
          cof<-t(as.matrix(lm1$coefficients))      
   
          b5<-summary.lm(lm1)
          se<-t(as.matrix(b5$coefficient[,2]))
          se1<-se[,2]
          cof1<-t(as.matrix(cbind(cof[,2],se1)))
          cof2a<-t(cof1)
          b1<-as.matrix(cof2a[,1])
          se11<-cof2a[,2]
          se11<-as.matrix(se11) 
   tstat[k,]<-b1/se11
          }



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