I also met this problem just now and solved it in this way. So I recorded it here, and I wish it be useful for others.
Scenario:
- Before I commit the code, revision: 100
- (Someone else commits the code... revision increased to 199)
- I (forgot to run "svn up", ) commit the code, now my revision: 200
- I run "svn up".
The error occurred.
Solution:
- $ mv current_copy copy_back # Rename the current code copy
- $ svn checkout current_copy # Check it out again
- $ cp copy_back/ current_copy # Restore your modifications