Just thought i'd mention a link that saved me a couple of hours this morning: if your mongrel does this on ImageScience invocations:

/usr/local/lib/ruby/gems/1.8/gems/RubyInline-3.6.7/lib/inline.rb:73:in `exit'
    /usr/local/lib/ruby/gems/1.8/gems/RubyInline-3.6.7/lib/inline.rb:73:in `rootdir'
    /usr/local/lib/ruby/gems/1.8/gems/RubyInline-3.6.7/lib/inline.rb:87:in `directory'
    /usr/local/lib/ruby/gems/1.8/gems/RubyInline-3.6.7/lib/inline.rb:257:in `so_name'
    /usr/local/lib/ruby/gems/1.8/gems/RubyInline-3.6.7/lib/inline.rb:297:in `load_cache'
    /usr/local/lib/ruby/gems/1.8/gems/RubyInline-3.6.7/lib/inline.rb:708:in `inline'
    /usr/local/lib/ruby/gems/1.8/gems/image_science-1.1.3/lib/image_science.rb:84
    ...
    

It means it doesn't find an environment variable INLINEDIR (or HOME, actually). It's used in the context of inline invocation of the FreeImage library (freeimage-VERSION.so). The function of this INLINEDIR directory is unclear to me, so i'll need to look into the whole RubyInline thing.

How to fix this: in config/environments/production.rb:

    #Ruby Inline Permissions Hackery
    ENV['INLINEDIR'] = RAILS_ROOT + “/tmp/.ruby_inline”
    

Thank you, thank you Mandarin Soda !