'xscreensaver -lock-mode' will pop up a dialog box that says "ERROR: RESOURCES NOT INSTALLED CORRECTLY" wherever text would normally appear. The colors are missing as well.
Works OK here on a base 5.2 install. You might try moving /usr/X11R6/lib/X11/app-defaults/XScreenSaver out of the way to see if it's causing problems, or deleting your ~/.xscreensaver file.