On the More Like This.. see the various very common complaints.. just to the right >>>
First one is good.. anything Pondini responds to listen. https://discussions.apple.com/message/17748380#17748380
A simple reboot of the whole network.. from off.. modem .. router/TC.. clients.. 2min gap will probably fix it.
If it keeps happening, tell us your OS. (Most likely Mountain Lion.. which has networking ability of wet string and a pair of tin cans).