Xbox, Media Center, and NAS - Please Help

I'm trying to use the Media Center on the Xbox to view media on my NAS.
When I access the Media Center on my PC I'm able to access the NAS.
Media Center starts on the Xbox, however, it says I don't have the permissions to access the NAS.

My guess is that I have to add the Xbox 360 as a user to the NAS but I don't know what that user would be.

Any help would be appreciated.

Thanks!

What are the permission settings for your shared folders on the NAS? I am not positive about using the Xbox to access a NAS since I don't own one. But I would think that if you set the permission on your Shared folder on your NAS to full control for Everyone that it may solve the problem.