Why is re-writing some of the system in Scala a debacle and or expensive? I haven't followed it too closely, but I got the impression that they have had success

Why is re-writing some of the system in Scala a debacle and or expensive? I haven't followed it too closely, but I got the impression that they have had success with it so far. Well, when you have a track record of screwing up on a fairly simple problem for 3 years straight then a switch of programming language will not magically solve that for you.