Forum: Rails deployment Crash on attempt to configure capistrano

I'm new with capistrano ant tried to configure my server usind:

   cap mongrel:cluster:configure

And got this error backtrace:

/usr/lib/ruby/gems/1.8/gems/capistrano-2.5.13/lib/capistrano/configuration/variables.rb:122:in
`method_missing': undefined method `sset' for
#<Capistrano::Configuration:0xb77f87dc> (NoMethodError)
  from ./config/deploy.rb:4:in `load'
  from
/usr/lib/ruby/gems/1.8/gems/capistrano-2.5.13/lib/capistrano/configuration/loading.rb:172:in
`load_from_file'
...

How to fix that problem?

Ok, it was a typo in my deploy.rb.

But fixing this, I run into the next trouble:

   cap mongrel:cluster:configure

ends now with

   the task `mongrel:cluster:configure' does not exist

Why this?

OK, next round in this deployment nightmare:

I configured my server, as decribed in "Agile Web Development with Rails 
Third Edition":

- installed rails etc.
- installed & configured apache2 w/ Passenger on a virtual Ubuntu 9.10 
server
- created a user 'oag' on the server and su'ed to oag
- created a git repository on the server and pushed my local repository
- run
    test -e ~/.ssh/id_dsa.pub || ssh-keygen -t dsa
    cat ~/.ssh/id_dsa.pub >> ~/.ssh/authorized_keys2
  on the server

- run
    cap deploy:setup
  localy - OK
- run
    cap deploy:check
  localy. Answer: You appear to have all necessary dependencies 
installed
- run
    cap deploy:migrations
  localy. Answer:
  * executing `deploy:migrations'
  * executing `deploy:update_code'
    updating the cached checkout on all servers
    executing locally: "git ls-remote oag@oag-server:git/wvz.git master"
oag@oag-server's password:
  * executing "if [ -d /home/oag/oag-server/shared/cached-copy ]; then 
cd /home/oag/oag-server/shared/cached-copy && git fetch  origin && git 
reset  --hard aeba71d5b7ce45e24cdb2bf052260fbc235b3a66 && git clean  -d 
-x -f; else git clone  oag@oag-server:git/wvz.git 
/home/oag/oag-server/shared/cached-copy && cd 
/home/oag/oag-server/shared/cached-copy && git checkout  -b deploy 
aeba71d5b7ce45e24cdb2bf052260fbc235b3a66; fi"
    servers: ["oag-server"]
Password:
    [oag-server] executing command
 ** [oag-server :: out] Initialized empty Git repository in 
/home/oag/oag-server/shared/cached-copy/.git/
 ** [oag-server :: err] Host key verification failed.
 ** [oag-server :: err] fatal: The remote end hung up unexpectedly
 ** [oag-server :: err] fetch-pack from 'oag@oag-server:git/wvz.git' 
failed.
    command finished
failed: "sh -c 'if [ -d /home/oag/oag-server/shared/cached-copy ]; then 
cd /home/oag/oag-server/shared/cached-copy && git fetch  origin && git 
reset  --hard aeba71d5b7ce45e24cdb2bf052260fbc235b3a66 && git clean  -d 
-x -f; else git clone  oag@oag-server:git/wvz.git 
/home/oag/oag-server/shared/cached-copy && cd 
/home/oag/oag-server/shared/cached-copy && git checkout  -b deploy 
aeba71d5b7ce45e24cdb2bf052260fbc235b3a66; fi'" on oag-server

The desaster begins after (successfully) entering the server user's 
(oag) password the second time.

Inspecting the auth.log of the server I don't find any notice on failed 
authentication.

What is the reason for this this "Host key verification failed"?
Where or how to find more information?