I believe that when WEBrick has trouble bringing up your Rails application, the WEBrick component that is supposed to print you a pretty error message has a bug and sometimes fails with this message:
"undefined method `bytesize' for #<Array>"
Starting the application in Passenger gave me a stacktrace in log/development.log
that pointed to the actual problem.
sqlite3
gem, but that gem wasn't in the Gem bundle.