subversion "working copy is corrupt" when trying to commit

I was having an issue today with a new SVN repository when trying to commit a bunch of files and folders I had copied in to the now-versioned project directory. Most of the files would commit, but a few would fail with "working copy is corrupt". I discovered while browsing the project directory (outside of my IDE, which hides .svn folders) that a few leftover ".svn" folders existed because some of the folders I copied in had come from another versioned project directory. I deleted the .svn folders, re-committed, and everything was ok!