In some cases, this error may come up if there's not enough preferred memory allocated to the Pro Tools application.What is a unique ID?Pro Tools 5.1 and later stamps each file that it records with a unique id. This way if there are several audio files on a system with identical names (i.e. "audio_01"), the session will know which its looking for. When Pro Tools can't link to a file and asks to locate it, the "require unique id" box can be checked if desired.