I had my Brother MFC-5890CN scanner/printer working with Ubuntu 10.*.
Now that I have upgraded to 12.04 LTS, the printer is still working but my scanner fails.
I found information that might help your problem from this link.
You could either run
After an upgrade from 10.04 LTS to 12.04 LTS, and because you say your printer is working we assume that the appropriate drivers are still installed. If not you may need to reinstall the scanner drivers. You can check this by running
Your libsane rules were probably overwritten by an updated version during the upgrade process. To make your Brother scanner accessible to all users add the following line to
Reboot your system for changes to take effect.
If the scanner still is not detected the Brother FAQ recommend to copy some driver files from