I went to check something into Subversion using Vi (i.e. Vim) as my EDITOR, and I got the following:
$ svn ciSure enough, even entering Vim and immediately exiting would return a non-zero exit status:
svn: Commit failed (details follow):
svn: system('vi svn-commit.tmp') returned 256
$ viI read somewhere that this might be because of a bad plugin. Sure enough, the following fixed it:
$ echo $?
mv doc/rails.txt plugin/rails.vim ~/.Trash