Im using spork 0.9.2 and rspec 3.0.0. When trying to run test rspec --drb I have an exception
rspec --drb
C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems
I had this same problem. Sans digging into the rspec3 source code, removing the --drb line from my .rspec file fixed the problem for me. Some Guardfile examples also have use of the --drb which causes issues for me. Once removed all tests work fine.