I got exactly the same error, using Emacs 24.3 and the newest cedet bzr version.
My solution is the following: Whenever something is decorated, the folding-mode will be enabled, too.
(load-library "~/emacs/cedet/cedet-bzr/trunk/cedet-devel-load")
(load-library "contrib/semantic-tag-folding.el")
(defun do-after-decorate () (semantic-tag-folding-mode t) )
(add-hook 'semantic-decoration-mode-hook 'do-after-decorate)
;; ...
(semantic-load-enable-excessive-code-helpers) ; also starts the decorate-mode when useful.
Works for me.