I got the same error, the reason is Ubuntu also upgraded svn lib files which are incompatible with older subeclipse. There is a simple fix. Uninstall the old subeclipse and install the newest version.
Select Help->Install New Software
Select “What is already installed” link in the lower right area. Uninstall all the packages for the current subversion.
Repeat the same Select Help->Install New Software and install the newest version from http://subclipse.tigris.org/servlets/ProjectProcess?pageID=p4wYuA
I used following update link : Eclipse update site URL: http://subclipse.tigris.org/update_1.8.x
For installation instruction see following.