ADAT is not properly referencing a clock source. Turn everything off, make sure all the cables have been properly connected between the ADAT, ADAT Interface, and the Pro Tools Audio Interface. Especially the Slave Clock Out from the ADAT Interface going to Slave Clock In on the Audio I/O, and Slave Clock Out from Audio I/O going to Slave Clock In on the ADAT Interface. Then power up the units in the following sequence: 1) ADAT (select Digital Sync - on original ADAT's, press Set Locate and Digital In on the front panel)2) ADAT Interface3) Audio Interface 4) ComputerIf the same problem persists, quit Pro Tools, trash the DigiSetup file from the System Folder, and repeat the power sequence. Then try toggling the clock source pop-up menu in the ADAT window, and back to the ADAT as clockmaster.