Installing gems with JRuby gets "marshal data too short" error

[Note to Blogger: Why was this unpublished? I see nothing that could cause offense and the notice gives no clue at all.]

Took me many hours to track this down. The error seems to be pretty generic, and various solutions have worked over the years:

http://stackoverflow.com/questions/5409675/marshal-data-too-short-error-message-while-installing-watir-webdriver-on-windo
http://stackoverflow.com/questions/19070698/how-to-modify-the-gemfile-marshal-data-too-short

Setting the verbose flag showed there was no network problem:

>gem install refile -V
io/console not supported; tty will not be manipulated
HEAD https://api.rubygems.org/api/v1/dependencies
200 OK
GET https://api.rubygems.org/api/v1/dependencies?gems=refile
200 OK
ERROR:  While executing gem ... (ArgumentError)
  marshal data too short

In the end it turned out to be JRuby in Ruby 2.0 mode.

>jruby --1.9 -S gem install carrierwave
io/console not supported; tty will not be manipulated
Fetching: carrierwave-0.10.0.gem (100%)
Successfully installed carrierwave-0.10.0
1 gem installed

I was trying to install refile to replace paperclip, which seems to be dodgy with Windows (requiring DevKit). Unfortunately, refile requires Ruby 2.1, so the gem cannot be downloaded with JRuby in 1.9 mode, and gem install does not work unless JRuby is in 1.9 mode. Great.

So I am looking at CarrierWave...