I now receive several error messages related to LISP code syntax errors when these same LISP files worked well in releases prior to the 2016 AutoCAD release.
I define custom Search File Support Paths in AutoCAD that include folders directly under my hard drive C:\ that includes LISP files (including an ACADDOC.lsp file that includes Autoload and Setvar statements).
Among these files is a custom PGP file that now shows syntax errors that worked on previous releases as well.
FYI: I turned 'OFF' the SECURELOAD setting with the understanding that it is not recommended.
One suggestion received by a colleague is to move/copy these custom files to the AutoCAD 2016 (installation) directory where the application's CUIX file(s) reside and see if that works.
COMMENT: It is amazing to me how the custom files' contents worked until 2016 that now alleges via command line feedback that there are LISP syntax errors e.g., malformed list on input, etc.