After installing SQL and try to Add a Workgroup in the ADMS Console, you are returned this error message
Subscribing workgroups must have the same version of SQL Server as the publishing workgroup.
In this instance, SQL 2008 R2 RTM was installed on both machines. However, on one machine Windows Updates had installed a patch for SQL on the publisher. But Windows Updates had installed the same patch on the Subscriber.
In the Vault Implementation Guide it asks "Are all Windows updates current on all servers?" in the Pre-Install Checklist. Obviously in this case there was a mismatch which was addressed by running Windows Update on both servers.
As mentioned in the Best and Worst practices of Vault...(see the categories on this blog) We recommend that once a machine enters production to turn OFF Windows Updates and lock it down. If this hotfix had been applied on one machine but not the other in a production environment, it would not be obvious to figure out the root cause of a failed replication.
It's best to turn off WU or there may be boo hoo ;-)