This error is usually caused by software driver problems. The most likely solutions:

• Corrupt Firewire controllers (if using a Firewire interface). Follow the instructions in Knowledgebase article number 30559 ("My Firewire interface is losing communication...").
• Currupt USB controllers (if using a USB interface). Unplug all USB devices, navigate to the Device Manager, and click on the "+" next to Universal Serial Bus controllers. Right-click and uninstall all Host Controllers. Reboot your PC and wait for all Found New Hardware Wizards to complete themselves. Reconnect your USB devices.
• Hubs and ports. If you are using a USB hub, try the interface directly into the computer. Also, if there are other available ports, try those. Sometimes a particular port works better with a particular device for no apparent reason.
• Outdated drivers. For LE systems, go to www.digidesign.com and select the version and OS os your Pro Tools system. Navigate to the downloads page, and download and install the latest updates. For M-Powered systems, go to www.m-audio.com and select your interface and OS from the list, then download and install the latest drivers.