Use Modify|Clean Up to clean up unfinished SVN operations for the selected directory (and all subdirectories). Cleaning up a working copy is necessary when the working copy becomes 'internally' locked (in contrast to file locks, see Locks). A working copy can become locked when certain SVN operations (like commit or update) are aborted. In general, cleaning up a working copy is a safe process.
A clean up may fail for the same reasons for which the preceding SVN operation has failed. This typically happens if certain files or directories can't be read or written. In such cases, please check whether other running processes might lock the file and whether file permissions have been set adequately.