uninitialized constant ActiveFedora::SolrService::YAML

[Bess Sadler]

I'm trying to deploy some ActiveFedora code on a server, and I'm hitting this error for code that was previously working in a development environment:

uninitialized constant ActiveFedora::SolrService::YAML

Here's the top of the stack trace:

[bess@sdr-fedora-dev sdr2]$ rake -T --trace
(in /home/bess/sdr2)
I, [2010-08-05T07:13:17.112567 #16386] INFO -- : FEDORA: loading SolrService mappings from /opt/ruby-enterprise-1.8.7-2010.01/lib/ruby/gems/1.8/gems/active-fedora-1.1.5/config/solr_mappings.yml
rake aborted!
uninitialized constant ActiveFedora::SolrService::YAML
/opt/ruby-enterprise-1.8.7-2010.01/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2503:in `const_missing'
/opt/ruby-enterprise-1.8.7-2010.01/lib/ruby/gems/1.8/gems/active-fedora-1.1.5/lib/active_fedora/solr_service.rb:83:in `load_mappings'
/opt/ruby-enterprise-1.8.7-2010.01/lib/ruby/gems/1.8/gems/active-fedora-1.1.5/lib/active_fedora/solr_service.rb:88
/opt/ruby-enterprise-1.8.7-2010.01/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'

Is it possible this is related to the mocha version dependency? What's a good strategy for figuring out where this is coming from?

Thanks!
Bess