WHy is rails so annoying to deploy?

List your current Ruby and Rails versions (i.e. the versions you are
upgrading from).

Check to ensure that you have all your gems configured properly and
perform a rake gems install to see if they are all installed properly.
Keep in mind that in production you are using RAILS_ENV=production rake
...

Start with the simplest things first.

What are you using with Rails, mongrel or passenger?

There are a lot of ways to handle this - I'd start with the patient one.