Não sei porque, mas isso permitiu o suporte DLNA para mim:
To enable HomeGroup members to access digital media
Open the server Dashboard
On the Dashboard Home page, click Set options for sharing.
On the Sharing Options page, click Share with Homegroup.
On the Change HomeGroup settings page, click Change settings.
For each shared folder, select the level of access that you want to allow users.
Click Apply or OK to save your settings.