One day I pressed in Eclipse Help -> Check for Updates (and I learnt that I should Never Ever update a software which works fine.)
Then in
I have had this happen before with Eclipse and the various SVN plugins that it supports. The SVN plugin, for some reason, sometimes looses the SVN connection. Your best bet is to simply delete the project and re-check it out of svn. If you have changes that need to be committed you can use the command line.
Another problem you may have is that your plugin and your repository are out of sync in terms of version numbers. I have had problems before using a plugin designed for svn 1.6.x and a repository that was still at svn 1.4 or 1.5.