Before I gave up last night in frustration, I sent off an email to tech support, essentially asking them why updating subversion works via command line, but fails when used in a post commit.
I got an email back, and the essence of the problem was that I can’t do what I was trying to do. (That being said, I already did it in three other places…so…???). But the solution was simple, and relatively painless. After writing a short CGI script, setting some permissions, and changing a line in the post commit file.
Total time spent: 8+ hours.
Time spent after email from tech support: 12 minutes.
So yes, sometimes it is as simple as talking to tech support.