When setting up a DFS replication group and later changing the drive letter of a drive for where DFS is replicating content you will see event id 6404 in the event log on Windows Server 2008 R2. The error in specific is:

The DFS Replication service failed to replicate the replicated folder at local path E:\DeploymentShare because the local path is not the fully qualified path name of an existing, accessible local folder.

Additional Information:
Replicated Folder Name: OsDeployment
Replicated Folder ID: C6E9C901-D6AE-47CA-A853-EE414186050A
Replication Group Name: OsDeploy-server1.contoso.com
Replication Group ID: C45CAA1D-0037-496F-881D-EC5DF596DF7B
Member ID: BF168723-6399-4229-9695-57E0352D43F9

To solve this make sure you show hidden files and folders and then delete the DfsrPrivate folder located in the root of the folder being replicated via DFS-R and then restart the DFS-R service and you are back in business.