Crash in actionpack on uploading files to the server

I have a working Rails application that allows users to upload files
in a couple of places. I recently converted from doing my development
on a Linux box to OS X 10.5 and also upgraded from Rails 1.1.6 to
Rails 2.1. I thought everything was working fine, but I just
discovered that the app crashes whenever I try to upload a file on the
OS X development system (it still works fine in production on Linux.)
Both systems are using Apache 2.x and are running mod_fcgid for
fastCGI.

When I try to upload a file on the OS X version I get the following in
the log:
/!\ FAILSAFE /!\ Wed Jun 11 17:33:03 -0700 2008
  Status: 500 Internal Server Error
  protocol error
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
request.r
b:573:in `read'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
request.r
b:573:in `read_multipart'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
request.r
b:547:in `loop'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
request.r
b:547:in `read_multipart'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
request.r
b:470:in `parse_multipart_form_parameters'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
request.r
b:400:in `parse_formatted_request_parameters'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
cgi_proce
ss.rb:80:in `request_parameters'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
request.r
b:304:in `parameters'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
request.r
b:22:in `request_method'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
request.r
b:35:in `method'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
routing/r
oute_set.rb:431:in `extract_request_environment'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
routing/r
oute_set.rb:384:in `recognize'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatche
r.rb:148:in `handle_request'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatche
r.rb:107:in `dispatch'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatche
r.rb:104:in `synchronize'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatche
r.rb:104:in `dispatch'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatche
r.rb:120:in `dispatch_cgi'
    /Library/Ruby/Gems/1.8/gems/actionpack-2.1.0/lib/action_controller/
dispatche
r.rb:35:in `dispatch'
    /Library/Ruby/Gems/1.8/gems/rails-2.1.0/lib/fcgi_handler.rb:103:in
`process_
request'
    /Library/Ruby/Gems/1.8/gems/rails-2.1.0/lib/fcgi_handler.rb:153:in
`with_sig
nal_handler'
    /Library/Ruby/Gems/1.8/gems/rails-2.1.0/lib/fcgi_handler.rb:101:in
`process_
request'
    /Library/Ruby/Gems/1.8/gems/rails-2.1.0/lib/fcgi_handler.rb:78:in
`process_e
ach_request'
    /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/
ruby/gems/1.8
/gems/fcgi-0.8.7/lib/fcgi.rb:612:in `each_cgi'
    /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/
ruby/gems/1.8
/gems/fcgi-0.8.7/lib/fcgi.rb:609:in `each'
    /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/
ruby/gems/1.8
/gems/fcgi-0.8.7/lib/fcgi.rb:609:in `each_cgi'
    /Library/Ruby/Gems/1.8/gems/rails-2.1.0/lib/fcgi_handler.rb:77:in
`process_e
ach_request'
    /Library/Ruby/Gems/1.8/gems/rails-2.1.0/lib/fcgi_handler.rb:76:in
`catch'
    /Library/Ruby/Gems/1.8/gems/rails-2.1.0/lib/fcgi_handler.rb:76:in
`process_e
ach_request'
    /Library/Ruby/Gems/1.8/gems/rails-2.1.0/lib/fcgi_handler.rb:50:in
`process!'
    /Library/Ruby/Gems/1.8/gems/rails-2.1.0/lib/fcgi_handler.rb:24:in
`process!'
    /Users/tsanders/code/DFDialogDatabase/public/dispatch.fcgi:24

In fastcgi.crash.log I get the following:
[11/Jun/2008:17:33:07 :: 16969] asked to stop immediately
[11/Jun/2008:17:33:07 :: 16969] stopping after explicit exit

And the apache error_log shows:
[Wed Jun 11 17:33:03 2008] [warn] (35)Resource temporarily
unavailable: mod_fcgid: write data to fastcgi server error
[Wed Jun 11 17:33:13 2008] [notice] mod_fcgid: process /Users/tsanders/
code/DFDialogDatabase/public/dispatch.fcgi(16969) exit(communication
error), terminated by calling exit(), return code: 0

As you can see this crashes before even getting to my controller code,
apparently while trying to parse the request passed in. My guess is
that there's some sort permission problem with creating the temporary
file to pass in params, but that's just a guess. I'm hoping somebody
out there who's more familiar with actionpack can tell me more. I
don't know that it's related to being on OS X particularly, but like I
said the exact same code and view works on a linux box, so it seems
the most likely culprit.