ArgumentError: dump format error(0x27) on model read

[bamkrs]

Using your example on a Heroku-App (rb 2.4.1) crashes when it tries to read the model.
On my local machine (rb 2.4.1) it runs perfectly.
I don't know what the dump format error(0x27) wants to tell me.

2017-10-15T13:59:47.919742+00:00 app[worker.1]: bundler: failed to load command: ebooks (/app/bin/ebooks)
2017-10-15T13:59:47.919896+00:00 app[worker.1]: ArgumentError: dump format error(0x27)
2017-10-15T13:59:47.919897+00:00 app[worker.1]:   /app/lib/twitter_ebooks/model.rb:49:in `load'
2017-10-15T13:59:47.919897+00:00 app[worker.1]:   /app/lib/twitter_ebooks/model.rb:49:in `block in load'
2017-10-15T13:59:47.919898+00:00 app[worker.1]:   /app/lib/twitter_ebooks/model.rb:48:in `instance_eval'
2017-10-15T13:59:47.919899+00:00 app[worker.1]:   /app/lib/twitter_ebooks/model.rb:48:in `load'
2017-10-15T13:59:47.919900+00:00 app[worker.1]:   bots.rb:127:in `load_model!'
2017-10-15T13:59:47.919900+00:00 app[worker.1]:   bots.rb:33:in `on_startup'
2017-10-15T13:59:47.919901+00:00 app[worker.1]:   /app/lib/twitter_ebooks/bot.rb:371:in `fire'
2017-10-15T13:59:47.919901+00:00 app[worker.1]:   /app/lib/twitter_ebooks/bot.rb:353:in `prepare'
2017-10-15T13:59:47.919916+00:00 app[worker.1]:   /app/bin/ebooks:361:in `block (2 levels) in start'