This may be a shared, read-only network directory, and is usually the folder where dten600.dll is located. 

The dtSearch Engine automatically loads external file parser DLLs from the viewers subdirectory of the HomeDir directory. If no Home directory is supplied, the dtSearch Engine will attempt to determine the location of its home directory using Windows system calls. Often this will work, but it is better to supply a specific Home directory.

DOptions Class