Error codes have been completely retooled in AutoCAD 2000. AutoCAD 2000 now offers Visual LISP which is a programming environment designed for AutoLISP. There, you'll find an environment that helps you find errors quickly, You can open Visual LISP by choosing Tools > AutoLISP > Visual LISP Editor. The Visual LISP Editor offers many of the tools you expect to find in a modern programming environment.
A discussion of Visual LISP is not currently available in this document. You can find a tutorial and reference guide built into Visual LISP by choosing Help > Visual LISP Help Topics. Click on the Contents tab to see a listing of topics including a tutorial chapter, on-line reference, and a developers guide.
Visual LISP is an advanced tool that expects the user to have a working knowledge of AutoLISP. You may want to work with the ABC's of AutoLISP until you feel comfortable with AutoLISP.