I just received an error ‘405 Method Not Allowed’ for a Subversion MKCOL request.
And googled this:
http://www.stereoplex.com/blog/subversion-mkcol-405-method-not-allowed/document_view

I just upgraded Apache (2.0 win32 to 2.2 x64) and php (5.2 to 5.3 x64) and I was fighting with mod_security2 all day to get SVN working (among other things).

Lesson: Always Update before Commit even if you are the only one using the repo 🙂