I've managed to create basic activity logging by following this tutorial (posted on module page):

I'm now trying to replicate the process for content created within a group, however it does not seem as straight forward as i expected, and i'm starting to wonder if its even possible in Rules? I'm aiming for a message of the format:

"User X posted content Y in the group Z"

I've taken a look at the message_og_example module which seems to handle all the message creation in code, so perhaps this is the only way? However when i enable the module and create a piece of group content i get the following error:

EntityMetadataWrapperException: Unknown data property og_membership__1. in EntityStructureWrapper->getPropertyInfo() (line 339 of /data/drupal7/sites/sustrans/site/sites/all/modules/contrib/entity/includes/entity.wrapper.inc).

In the message_og_example i notice the group field is and EntityRefence field; is there a reason why it's not simply Group Audience?

Lots of questions - if anyone can shed any light it'd be greatly appreciated