I was getting this annoying error when setting up lyra captcha (great product by the way!).
Element CAPTCHA is undefined in a Java object of type class [Ljava.lang.String
Well after a little silent swearing and a few deep breaths, I figured it out.
In the captcha folder there is an application.cfm file – edit this making the application name the same as your general application name (defined in application.cfc or application.cfm).