UnderrunErr (a DSP needed audio data from the disk drive and didn't get it soon enough).- Slow CPU.- DAE <1.05 with an external clock (Digital sync, SSD, VSD) was prone to this. Install DAE 1.05 or later.- Bad clock in the system.- Unstable SMPTE source.- Problematic hard drive (bad blocks, fragmentation, or a drive that has not been recently formatted might contribute to this).- Real time Extension or CDev (users have reported this with After Dark).- Verify Apple System Update 3.0 (or later) is installed.- Loose chip(s) on SysAxe. Put the SysAxe on a flat surface and push down all socketed chips.