'cap express deploy:long' is failing

[Neil]

Hi EY express

I've been struggling to get 'cap express deploy:long' to deploy
successfully, it keeps telling me that I need to install Rails 2.1,
which I have already done. 'cap express deploy' will run with a
'success', however, when I refresh http://express.local/, I see the
apps 500 template but with the Erb tags printed out in HTML (so I know
I'm getting to the repo ok). Visiting http://express.local:3000 will
flash the Rails index.html for one request, and then throw an error.

The app is up & running in production, so I'm wondering what could be
wrong with deploying to express. Are there any initial steps I can
take in the troubleshooting process? I don't know where to look first
- this Rails 2.1 thing has really thrown me - could it be giving me
the Rails 2.1 because another gem is missing, perhaps? I've made sure
that all the gems from the production slice are also installed on the
express slice - the only one missing is 'eyrubygems' which I don't
seem to be able to find through 'gem install eyrubygems'.

Any suggestions?