I see that this is an old issue and a best answer has already been found, but I recently came across this same issue and solved the problem by updated the original Paperclip.options information in development.rb
to read:
Paperclip.options[:command_path] = 'C:\Program Files\ImageMagick-6.9.0-Q16;C:\Program Files (x86)\GnuWin32\bin;'
You must add both ImageMagick and File to the path. Omitting the reference to File produces the original referenced error message "Avatar has an extension that does not match its contents"
, but omitting ImageMagick produces the error messages mentioned by Matt Gibson, "Paperclip::Errors::NotIdentifiedByImageMagickError."
I'm not totally sure this is a case of File not being installed or installed improperly, but rather that no one ever explicitly mentions that both references need to be added to the PATH. I know this seems like a relatively "common sense" type of issue for someone who has been coding for a while, but for a newbies, sometimes things like this need to be spelled out. I only figured it out because I used a SUPER OLD tutorial to install Ruby/ Rails on my machine and got very familiar with PATH's and the command line, while newer tutorials don't go into great detail about that kind of stuff and instead want to get you "up and running as quickly as possible...." even if the side affect is that you don't necessarily understand what you were doing.