Comment 3 for bug 415101

Sorry, that did not come out so good. In more detail, after you enable debug-on-error, try to visit a C buffer and attempt to open the C menu; this (I speculate) ought to produce a *Backtrace* buffer which you can save to a temporary file and attach here. (Press q in the *Backtrace* buffer to discard it. M-: (setq debug-on-error nil) to turn off debugging.) Sorry for the sloppy instructions, and thanks in advance.