If this error afflict your quiet development day, I’m sorry 
I had this problem today and I solved in few steps:
- make a backup of the working copy in a different directory
- delete only the corrupted directory from your working copy
- make an svn update
- copy back only the modified files you need from the backup copy to the current working copy
- commit your changes
Now breath deeply and take a cold shower: I suppose you must be sweat!
