Is your Mint system 32 bit or 64 bit? If its 64 bit, see if the pre -reqs are installed. See this link
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http://welcome.solutions.brother.com...efore.html#004
Follow the link for Ubuntu 64 bit to see the pre-reqs. Install them if they are missing.
Brothers site tells you how to install the lpr driver or the cups wrapper driver. Have you followed those instructions?