Auto Action: Message in the stream (New member)

Hi, I'm currently trying to set up Auto Action, but I'm stuck. There's already a preset action: when a new member registers, a message is generated in the stream (XXXXX has registered). I've deactivated this action because I want to create a different, more personalized one. I'm using:
Global
on AfterUserRegistration
Type: CB Activity
User: Automatic
ACL: All
Action
Mode: Activity
Method: Create
Stream: Recent Activity
Published: 1
Title: My Title
Message: My Message
This isn't working; the action isn't firing and is always stuck at zero. Can you point me in the right direction? I'm obviously doing something wrong.

Thanks a lot,
Thomas

Are there any examples or lists I can look at to learn from?

The below would mimic what the internal behavior is doing.

Global
Triggers: onAfterUserRegistration
Type: CB Activity
User: Automatic
Access: Everybody
Action
Mode: Activity
Method: Create
Stream: Profile Activity
Asset: profile.[user_id].registration
Load By: None

That asset would just result in the same title displayed as the internal activity, which is "joined the site". Note that is a language string so you could just override it for example. To avoid that you could create your own asset. Below for example would work fine.

Asset: profile.[user_id].registered
Title: My Title
Message: My Message