incompatible marshal file format (can't be read) format version 4.8 required; 0.0 given

Have you tried clearing assets? bundle exec rake assets:clean

And then recompile: bundle exec rake assets:precompile

Are you somehow mixing up Ruby versions? Maybe you are precompiling with 1.9 and running Rails through Passenger or something with 2.0?

I had to delete the sass and sprockets folders in rails_root/tmp/cache.

Fix: change the secret key base to invalidate all sessions, especially after Rails upgrade.