selected svn connector library is not available or cannot be loaded

• Help > Install New Software...
• Paste in the URL http://community.polarion.com/projects/subversive/download/eclipse/2.0/update-site/
• Select the connector you wish to install (I usually go with SVNKit). You need to select both the wanted connector and the generic "Subversive SVN Connectors" item.
• Click Finish

You should be able to use your repository now, but if not :

• Go to Window > Preferences
• Browse to the Team > SVN item
• In the SVN Connector tab, make sure that SVNKit is selected as the active one.