The VS-1680 stores data such as audio data or parameter values on disk in units
called files. In order to manage large numbers of files, the VS-1680 keeps
lists of file names and the locations on disk in which the data of these files
is stored. These lists are called directories.
The "IllegalDIR" message will appear when this list is incorrect. For example,
this message will appear if the data of a certain file is supposed to be
recorded in an area of the disk which does not actually exist, or if the list
itself becomes permanently unreadable.