When I type 'C-c , J' (semantic-ia-fast-jump) in a buffer (c-mode, with file tree.def from GCC source tree), I get the following message.

semanticdb-find-translate-path-default: Wrong type argument: stringp, nil

if the buffer has fundamental-mode:

semantic-ctxt-current-symbol-default: Wrong type argument: syntax-table-p, nil

similar reports:

http://lists.gnu.org/archive/html/bug-gnu-emacs/2010-07/msg00541.html
http://sourceforge.net/mailarchive/forum.php?thread_name=4C118357.9010105%40siege-engine.com&forum_name=cedet-semantic