Mongrel_cluster with prefix

If i try to start mongrel_cluster with a prefix a receive this error
message.

/usr/lib/ruby/gems/1.8/gems/activesupport-2.3.2/lib/active_support/dependencies.rb:440:in
`load_missing_constant’: uninitialized constant
ActionController::AbstractRequest (NameError)

Without a prefix Mongrel Cluster works fine.

Can anyone help me.

thanks
Michael