Apple TV says "No content was found in this library" when viewing iTunes library

Hi,

I have:

1) An external drive holding my iTunes media

2) A Mac mini to which the external drive is connected. This Mac mini is accessible via Dynamic DNS.

3) A Macbook Pro laptop

4) A 3rd generation Apple TV

I have all the software on both machines updated to the latest. I can mount the external drive onto my laptop using AFP. I have Home Sharing turned on in iTunes on both machines. I believe I have all the proper ports open on my wireless router:

1) TCP ports 123 (NTP), 3689 (Home Sharing) and 548(AFP)

2) UDP port 5353 (Home Sharing)

When I try to access my iTunes library through my Apple TV from my laptop, the Apple TV shows me all my media.

When I try to access my iTunes library through my Apple TV from my Mac mini, the Apple TV says "No content was found in this library".

Can anyone suggest what piece I'm missing from the setup on my Mac mini, or perhaps my wireless router?

Thanks,

Jason Mazzotta