R error in write.table >> Error in sc[[length(sc) - 7L]][[1L]] == "example"

I have a data.table object named dat where if I try write.table(dat,'test.txt'), I get this bizarre error:

'Error in sc[[length(sc) - 7L]][[1L]] == "example": comparison (1) is possible only for atomic and list types'

Following the stack trace takes me to cedta.R

cedta.R is way over my head. What is going on here and how do I address this issue?

In context, I read some data from a text file with fread(), then I select some rows from the table using a conditional, then I want to write the filtered table to a new text file. Pretty simple, I'm very confused what's wrong here.

dat <- fread(ptx, skip = 10, header = FALSE)
names(dat) <- c("X", "Y", "Z", "Intensity", "R", "G", "B")
ptx_header = readLines(ptx,n=2)
ncols = as.integer(ptx_header[1])
nrows = as.integer(ptx_header[2])

if (reducePtx==T){
  # Remove every other point from PTX file
  npoints = dim(dat)[1]
  cols = 0:(npoints-1) %/% ncols
  rows = rep.int(0:(nrows-1),ncols)
  dat1 = dat[cols%%2==0 & rows%%2==0,]
  remove(cols)
  remove(rows)

  # Write output ptx file
  ptx_out = paste0('reduced_',ptx)
  write.table(dat1,ptx_out,append = T,sep=' ',quote=F,row.names = F,col.names = F)}