The 'lock' LED does not light when syncing my ISA 428 to 256X super clock from Pro Tools. Is something wrong?

When syncing to superclock the 'lock' LED does not actually light and should not be used as an indicator of lock. If you can get a clean digital audio signal out of the 428 and into Pro Tools when set to sync to superclock then you know it is locked. If you get digital noise or nothing at all then check that the sample frequency and bit depth settings are the same on both the 428 and in Pro Tools and set the clock source in Pro Tools to internal/superclock.