[R] In R 2.14.1, what does wrong sign in 'by' argument mean?

[bioinformatics]

Here is my code


    slidingwindowplotATGC = function(windowsize, inputseq) 
    {

    starts = seq(1, length(inputseq)-windowsize, by = windowsize)
    n = length(starts)
    chunkGs = numeric(n)
    chunkAs = numeric(n)
    chunkTs = numeric(n)
    chunkCs = numeric(n)
    for (i in 1:n) { 
        chunk = windowsize[starts[i]:(starts[i]+9999)]
        chunkG = sum("g" == chunk)/length(chunk)
        chunkA = sum("a" == chunk)/length(chunk)
        chunkT = sum("t" == chunk)/length(chunk)
        chunkC = sum("c" == chunk)/length(chunk)
	  chunkGs[i] = chunkG
        chunkAs[i] = chunkA
	  chunkTs[i] = chunkT
	  chunkCs[i] = chunkC
	}   
   
plot(starts,chunkGs,type="b",ylim=c(min(min(chunkAs),min(chunkTs),min(chunkCs),min(chunkGs)),max(max(chunkAs),max(chunkTs),max(chunkCs),max(chunkGs))),col
= "red")
    points(starts,chunkTs,col = "blue")
    points(starts,chunkAs,col = "green")
    points(starts,chunkCs)
}


Im getting the following error message,

    Error in seq.default(1, length(inputseq) - windowsize, by = windowsize)
: 
      wrong sign in 'by' argument


which I never got before when running codes of this sort, infact I re ran
old code that worked perfectly before, except this time Im getting this
error message which doesn't seem to make any sense at all! I need help with
this before I go completely insane... Maybe Im just bad at this program, but
it seems to me that it has a mind of its own... I was also getting an error
message before regarding the ylim function, stating that it needed to be a
finite value, which is what I was giving it? HELP!!!

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