Update: Do not forget to get rid of autogenerated backgroundrb etcetera files that were generated during last run of rake backgroundrb:setup.
A plain fork() is evil under Ruby and hence there are some issues with memory usage of BackgrounDRb. I have made some changes to packet library so as it uses fork and exec rather than just fork for better memory usage. However, there were quite bit of changes and BackgrounDRb is affected by them. You can try bleeding edge version as following.Also you need rspec for building packet gem.
clone the packet git repo:
git clone git://github.com/gnufied/packet.git cd packet;rake gem cd pkg; sudo gem install --local packet-0.1.6.gem
Go to your vendor/plugins directory of your rails directory and remove or
backup older version of backgroundrb plugin and backup related config
file as well.
from vendor/plugins directory:
git clone git://github.com/gnufied/backgroundrb.git cd RAILS_ROOT rake backgroundrb:setup ./script/backgroundrb start
Let me know,how it goes.