looking at the code, the only way it would not raise that error would be if you set manage_puppetca setting to false.

a simple solution could be:

diff --git a/app/models/host/managed.rb b/app/models/host/managed.rb
index cb3d468..8950920 100644
--- a/app/models/host/managed.rb
+++ b/app/models/host/managed.rb
@@ -223,9 +223,8 @@ class Host::Managed < Host::Base
   def handle_ca
     return true if Rails.env == "test" 
     return true unless Setting[:manage_puppetca]
-    if puppetca?
-      respond_to?(:initialize_puppetca,true) && initialize_puppetca && delCertificate && setAutosign
-    end
+    return true unless puppetca?
+    respond_to?(:initialize_puppetca,true) && initialize_puppetca && delCertificate && setAutosign
   end

The patch seems to help:

Started GET "/unattended/provision?token=401a421e-6c98-4af9-bf35-e8d8cb292c0c" for x.x.x.x at Mon Jul 22 17:29:44 +0200 2013
Processing by UnattendedController#provision as */*
  Parameters: {"token"=>"401a421e-6c98-4af9-bf35-e8d8cb292c0c"}
Found catest.test.xxx.de
  Rendered inline template (30.9ms)
Completed 200 OK in 73ms (Views: 31.3ms | ActiveRecord: 4.4ms)

Thanks for testing!