roll back,merge and tree confilct

Hi,
   I need to roll back to a particular version. I read this post
http://jacwright.com/blog/75/how-to-roll-back-changes-using-subversion/
It tells me to use merge to roll back. However, I failed due to a so-called
tree conflict. I don't know how to solve that problem.
I tried svn update and update seems successful. But after svn update, I
still cannot use svn merge to roll back.,
Error: Attempt to add tree conflict that already exists.

Thank you.
Received on 2011-04-11 04:00:55 CEST