I'm running into this problem because my company's svn repository isn't up to date. Is there a way to downgrade to svn 1.5 in Karmic? It doesn't appear that 1.5 is even an option in the apt repository.
You probably want to install a local copy of Subversion. There are two ways to do this:
Here's a search of the Subversion packages in various Ubuntu repositories. You might be able to install one of those packages directly, but watch out for wonky dependency issues. I'd guess that the Jaunty packages have the best chance of working out-of-the-box; for older releases, you might need to compile your own .debs from the sources for those packages.