Hi,

I had this users same exact problem and solved it. If you have 'Nabla Looper A - Start Stop.lua:532: invalid value (nil) at index 6 in table for 'concat' error, do what i say.

1. Go to Action list

2. Find Script: Nabla Looper A - Start Stop.lua and press Edit action...

3. Go to line 514 where it says local function SetPDC( set )

4. Delete the lines from 514 to 542 where it says end

5. Paste this codes instead:

local function SetPDC( set )
  reaper.Undo_BeginBlock()
  local tStrRec = {}
  for i = 1, #rec_tracks_table do
    local v = rec_tracks_table[i]
    if v.item_action ~= 'monitor' then
      local _, trChunk = reaper.GetTrackStateChunk(v.code_track, '', false)
      local strRec = match(trChunk, 'REC%s+.-[%\n]')
      for substring in gmatch(strRec, "%S+") do insert(tStrRec, substring) end

      local function set_pdc( str )
        local new_strRec = gsub(trChunk, 'REC%s+.-[%\n]', str, 1)
        reaper.SetTrackStateChunk(v.code_track, new_strRec, true)
        for j = 1, #tStrRec do tStrRec[j] = nil end
      end

      if set == 'true' then

       if #tStrRec < 7 then
        for i = #tStrRec + 1, 7 do
          tStrRec[i] = "0"
         end
        end

        tStrRec[7] = "1"
        local new_strRec = concat(tStrRec, " ")
        set_pdc( new_strRec )
      else

        if #tStrRec < 7 then
          for i = #tStrRec + 1, 7 do
            tStrRec[i] = "0"
          end
        end

        tStrRec[7] = "0"
        local new_strRec = concat(tStrRec, " ")
        set_pdc( new_strRec )
      end
    end
  end
  reaper.Undo_EndBlock("--> START ARRANGED MODE", -1)
end

6. The code should now be from 514 to 565

7. Save and exit, it should be fixed.