403 Error on _some_ file uploads in 4.1RC2

[ideaoforder]

Hello,

On one specific page, I'm getting a 403 Access Denied error when uploading files in a Rails app--the request doesn't even seem to hit the Rails app (i.e. nothing shows up in the log), so it's choking before it hits the app.

Everything works fine locally. And everything works fine on other pages running pretty much identical code. Even more strangely, everything seems to work fine when uploading from computers that have Rails installed, but not on computers that don't.

I haven't been able to pinpoint anything in the logs, but I feel like this is an issue with Rack, which had to be patched slightly to make LSAPI work with Rack 1.0.1 (required for Rails 2.3.5).

Any ideas on this?