My team ran into this problem last week, you may consider checking the status light, depending on whether or not it's flashing and how frequently can help tell you what's wrong. You may also want to connect directly to your computer using an Ethernet crossover cable (that's what worked for us). Finally we followed all of the troubleshooting steps outlined at the bottom of this page
http://wpilib.screenstepslive.com/s/...ging-your-crio