render :partial 'foo.html.erb' # renders '_foo.html.erb'

http://dev.rubyonrails.org/ticket/8076

"The new naming scheme for template (eg. .html.erb) does not seem to work for partials. When using :partial => 'form' a filename "_form.html.erb" is not recognized. "

Rails now requires the partial to be referenced by dotted format

Rendering partials in Rails 2.0

rails, ruby

Rails