Given that your system is looking for an incomplete file, either the manifest for your style sheets does not get precompiled, or this is not your answer:
I had a similar problem with a system that worked fine in development, but not in production with precompiled assets. I used a secondary layout for my registration / on pages that included a custom manifest file for style sheets. Since rake assets:precompile only compiles application.css by default, my signup.css not precompiled, and I got an error similar to yours when I got to the login page.
I fixed this by adding the following line to config/application.rb :
config.assets.precompile += %w(signup.css)
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