The comment form of this blog was broken the last two days. The reason was that I disabled the no_cache parameter in the install tool. It seems the ve_guestbook extension somehow relies on this parameter. The comments are now working properly again. Sorry for the inconvenience.
Meanwhile I found out that ve_guestbook disables complete caching of pages with the guestbook form. I don't like that and it's not necessary. The plugin could be rendered as USER_INT instead of disabling page cache. I sent a bug report #12131 and appended a patch which fixes this issue: http://bugs.typo3.org/view.php?id=12131