Apple TV, content from two users on same mac My parents have an iMac that they share using fast user switching. They each have an iTunes library, where mom keeps the pictures from the family's digital camera and her music collection, and dad maintains his music and the family's movie collection. Also, they each have an iPhone, which is synced to their respective music library. 

We recently got them an Apple TV, so that they'd be able to enjoy the content on their tv. We've gotten both picture viewing, music streaming and movie watching work, but the problem is that all content is not accessible at the same time.

To me it appears that the culprit is the fast user switching. Both libraries appear on the Apple TV, but usually only one of the libraries is accessible. I have not been able to establish a pattern with regards to who is the active user on the iMac, i.e. it does not appear to matter if dad's the foremost user on the mac when trying to access his library from the tv (or if mom's foremost when trying to access dad's library).

Any suggestions as to what can be done to solve this problem? The goal is that all content should be accessible from the Apple TV at all times.

They are using iTunes 10.5.3, unfortunately I can't tell the software version of the AppleTV right now.
Firstly, in order for AppleTV to see the iTunes Library a user must be logged in and running iTunes. If both of these are not present then AppleTV won't work.

Since they are on the same physical Mac might I recommend combining the iTunes Media folder and placing it in the /Users/Shared/ directory. As all users have access to the Shared directory the actual media files wouldn't be duplicated and they can each maintain their own iTunes Library. After moving the iTunes Media folder to the Shared folder you will need to go into iTunes Preferences for each user and under the Advanced tab select the new iTunes Media folder location.