FAILSAFE error with uploads

I've just upgraded a production web site with some new code to handle
file uploads, using both the standard post technique and swfupload.
This code was working perfectly in my development environment, and I'm
not sure what I should ever start to look for. Here's the stack dump:

/!\ FAILSAFE /!\ Wed Feb 06 19:13:41 -0700 2008
  Status: 500 Internal Server Error
  protocol error
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
request.rb:510:in `read'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
request.rb:510:in `read_multipart'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
request.rb:445:in `parse_multipart_form_parameters'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
request.rb:383:in `parse_formatted_request_parameters'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
cgi_process.rb:78:in `request_parameters'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
request.rb:287:in `parameters'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
request.rb:22:in `request_method'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
request.rb:35:in `method'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
routing.rb:1483:in `extract_request_environment'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
routing.rb:1424:in `recognize'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
dispatcher.rb:170:in `handle_request'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
dispatcher.rb:115:in `dispatch'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
dispatcher.rb:126:in `dispatch_cgi'
    /my/app/web/vendor/rails/actionpack/lib/action_controller/
dispatcher.rb:9:in `dispatch'
    /my/app/web/vendor/rails/railties/lib/fcgi_handler.rb:101:in
`process_request'
    /my/app/web/vendor/rails/railties/lib/fcgi_handler.rb:149:in
`with_signal_handler'
    /my/app/web/vendor/rails/railties/lib/fcgi_handler.rb:99:in
`process_request'
    /my/app/web/vendor/rails/railties/lib/fcgi_handler.rb:77:in
`process_each_request'
    /usr/local/lib/ruby/site_ruby/1.8/fcgi.rb:612:in `each_cgi'
    /usr/local/lib/ruby/site_ruby/1.8/fcgi.rb:609:in `each'
    /usr/local/lib/ruby/site_ruby/1.8/fcgi.rb:609:in `each_cgi'
    /my/app/web/vendor/rails/railties/lib/fcgi_handler.rb:76:in
`process_each_request'
    /my/app/web/vendor/rails/railties/lib/fcgi_handler.rb:50:in
`process!'
    /my/app/web/vendor/rails/railties/lib/fcgi_handler.rb:24:in
`process!'
    /my/app/web/public/dispatch.fcgi:26

Regardless of how the file is uploaded, this is the termination point
of the error:

/my/app/web/vendor/rails/actionpack/lib/action_controller/request.rb:
510:in `read'

which is this line:

status = body.read(boundary_size)

So, it seems that the upload is barfing when trying to read the
streaming content.

This happens with both Firefox and IE. Does anyone have any ideas why
this is happening? Help!

I'm still struggling with this one - any ideas?

Apparently, this issue is related to the combination of Apache/
lighttpd and fastcgi. Dropping lighttpd and fastcgi in favour of
Mongrel has solved the problem.

I'd still like to know why this problem just started happening - what
did I change to break my code?

Ah well - it's working now, so it's certainly a lower priority
now....