tommtomm,
No, the two blue non-perforated lines on your stamp are the "cut lines" intentionally not perforated. Your stamp is entirely normal. It is not an error. The title on Don's article could be clearer if it said more directly "Red line and green lines stamps are not rare errors", because readers tend to look past the quote marks and see what they want to see. (LOL, wkusau was typing at the same time I was!)
Add: I will quibble slightly with what wkusau states:
Quote:
collectors have never liked them thus they are less expensive
In the 1920s-50s, Collectors did avidly collect these cut line stamps to reconstruct miniature "panes of 9". I have posted portions of this catalog before where 2-lined stamps held a decent premium, now almost completely gone out of style:
