You're going to delete the whole directory containing the problem. Choose a reasonably small directory that completely contains the problem.
First, make sure everything else of value in the directory (especially including the file(s) you're having trouble with) is committed to the repository or backed up somewhere else on your computer.
Now just manually delete the directory (without using SVN, just however you normally delete files).
Go to the directory above it and say
> svn update
Your working directory should now be refreshed with a clean copy of the probably formerly problematic directory.
Copy back in any files you backed up. If they're the same as what got committed to the repository then you and svn can forget about it. If they're different, it should be just like any other time you made a change in your working directory. (E.g., you can "svn diff" or "svn commit" or keep editing the file(s).)
