For future reference for those searching mail archives..
This error is because the files were checked out with http not https.
Rather than checking out all over again with https, you can use the svn
switch command to switch your existing checkout from http to https.
> So I just tried to merge the last change to the M4 branch, and
> when I commit I get this:
> svn: Commit failed (details follow):
> svn: MKACTIVITY of
> '/repos/asf/!svn/act/8e9df19d-ccfb-0310-b494-e4c675c3586b': 403
> The gibberish varies each time. I'm confused -- I was able to
> alter the branch yesterday. Any ideas?