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>"

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Starting the application in Passenger gave me a stacktrace in log/development.log that pointed to the actual problem.

Possible causes discovered by looking at the logs

• A Rails plugin would require the sqlite3 gem, but that gem wasn't in the Gem bundle.
• Rack only parses 65536 form params by default
• Problem can occur when using the integrated Ruby Mine Debugger: Try to restart the server without debugging mode