We have a continous build which polls the SVN fpr changes every minute and then does an update and builds and sends any errors to the committer.
Today we accidently checked in changes that made our build script destroy one of the .svn directories which destroys the working copy so future svn updates failed.
If the update fails the last checked out revision is older than the lastest availabe which makes the SVN trigger to trig every time and retry to update over and over again casing hudson to try and build mevery minute and spamming the last committer with mails.

One SVN change should only be able to trigger one build.