Internal server error 500 using SVNKit (hudson problem)

Had trouble checking out from SVN on a Hudson client, the error rather cryptically just “internal server error: 500”. The exact same project, but checking out onto a different client, worked fine.
After some hunting around and trying various stuff in vain, I deleted the SVN authentication details stored on the client at %APPDATA%/subversion/auth/svn.simple and the checkout started worked properly.
I assume this is because the client in question had been previously used to check out from SVN with other applications and that the cached credentials were somehow not-quite-right, but that’s speculation.