Mac OS X 10.5: Back to My Mac cannot reach a sleeping Mac
Symptoms
Back to My Mac will only work when your computers are awake. If you have set your computer to sleep after a time, it will not automatically wake up when you try to contact it from a remote location via Back to My Mac.
If your computer goes to sleep, its connection to the Internet will be interrupted, which in turn will prevent remote Back to My Mac connections.
Products Affected
Back to My Mac, MobileMe
Resolution
In Energy Saver preferences, you can use display sleep or enable "Put the hard disk(s) to sleep when possible", but you should leave the "Put the computer to sleep when it is inactive for" slider on "Never" for each computer you use Back to My Mac with.
Note: You can set a different time for the display to sleep. Sleeping your display will save power and it will not affect your network connection or Back to My Mac if your network connection remains active.