Hi Mateusz,
It looks like the file is not being identified properly as a text file. We run `file --mime-type -b <filename>` on the server to try to determine a suitable file type, so it could be that:
1) `file` is not available on the server
2) The mimetype is not coming back as text/* (such as text/plain, text/x-robot, etc.).
What OS is Review Board installed on? Can you see if `file` can be run, and if so, can you try uploading the file to the server and running the above command on it and show me what it says?
Christian