What the heck - corruped mongrel server?

See the patch to active_support in changeset 6426, below. Not sure if
your problem is the same, but sounds as if it could be. I didn't move
all the way to edge, just applied the one patch, and my NoMethodError
problems have vanished.

<http://dev.rubyonrails.org/ticket/6720>
<http://dev.rubyonrails.org/ticket/6951>
and
http://dev.rubyonrails.org/changeset/6426