I'm sorry about the issue. Was scanning working fine previously with this printer and this macbook with Yosemite 10.10.2 version?
Have you tried to trash the Brother / ControlCenter application from Applications in Finder, then download / reinstall the Scanner Driver at the Brother website below and check?
If that does not work, can you open Finder, then open Applications, then open the Image Capture application, and use it to scan?
Please reply at the box below to continue troubleshooting. Thank you.