That TW document uses "TiddlyWiki Classic" ("TWC") v2.1.3, which is from November, 2006.
Since then, TiddlyWiki has been *completely* re-written from the ground up as "TiddlyWiki 5" (based on modern HTML5 standards), which is not backward-compatible with the "Classic" features, functions, and macros
Specifically, as noted by Mark S, the <<today>> macro no longer exists, and has been replaced by the <<now>> macro.
You can find documentation of the current features and syntax on http://TiddlyWiki.com.