Funky error message on OS X

I’m following along with Peepcode’s guide to using Capistrano to deploy
Rails apps right now, but I’ve hit a snag and I have no idea what to do
to fix it. When I try to “sudo gem install railsmachine
–include-dependencies,” the machine thinks for a few seconds, then
gives me this funky error message:

ERROR: While executing gem … (NoMethodError)
undefined method `refresh’ for #Hash:0x1107ff4

Has anybody seen this before? I honestly haven’t an inkling of what this
means nor how to remedy it.