Attempt to add printer was done on a fresh install of Quirky Tahr 6.0.5, which is a 32-bit version of Quirky.The "internal server error" has nothing to do with the Brother driver and everything to do with the CUPS setup in Quirky. Are you doing this from a clean install? Have you added any other packages like web browsers? Are you using a 32bit Quirky?
You should post your problem in the Quirky thread.
The only package added was debbi-1.2.pet. Specifically no browsers were added.
O.K., I'll give the Quirky thread a try.