Subscript out of Bounds

I currently have this code:

for(j in 2:n){
   for(i in 1:(j-1)){

     # Make sure the inputs are for the matrix "m"
     input1=rownames(m)[i]
     input2=colnames(m)[j]

     q=t[(t$Rec1==input1&  t$Rec2==input2),output]

     if(length(q)==0){
       q=t[(t$Rec1==input2&  t$Rec2==input1),output]
     }

     m[i,j]=mean(q)
     m[j,i]=mean(q)
     m[j,j]=mean(q)
}}

I already created a 20x20 matrix "m" and have the rows and columns made up:

m=matrix(data=NA, nrow=rl, ncol=rl, dimnames=list(R1=rec.list, R2=rec.list))

the length of a column in the matrix is 20
the length of n is 430

When I run this, the error: "Subscript is out of Bounds" appears when it
reaches the m[i,j].
Checking again, the issue is primarily with "j"

How would I go about fixing this issue (nevermind the "mean(q)", as I don't
even know if that works and didn't get the chance to explore it)?