title: Failed: RuntimeError: Saving diagram failed! when running rake erd command
body: <p>I am trying to rake erd to generate diagrams for models in my rails application. I am on windows 7 and graphviz is installed</p>
  
  <p>When I run </p>
  
  <pre><code>rake erd OR rake erd filetype=dot
  </code></pre>
  
  <p>I am getting following error</p>
  
  <pre><code>$ rake erd --trace
  ** Invoke erd (first_time)
  ** Invoke erd:generate (first_time)
  ** Invoke erd:options (first_time)
  ** Execute erd:options
  ** Invoke erd:load_models (first_time)
  ** Execute erd:load_models
  Loading application environment...
  ** Invoke environment (first_time)
  ** Execute environment
  Loading code in search of Active Record models...
  ** Execute erd:generate
  Generating Entity-Relationship Diagram for 6 models...
  rake aborted!
  Saving diagram failed!
  Verify that Graphviz is installed and in your path, or use filetype=dot.
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rails-erd-1.1.0/lib/rails_erd/diagram/graphviz.rb:198:in `r
  escue in block in &lt;class:Graphviz&gt;'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rails-erd-1.1.0/lib/rails_erd/diagram/graphviz.rb:190:in `b
  lock in &lt;class:Graphviz&gt;'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rails-erd-1.1.0/lib/rails_erd/diagram.rb:142:in `instance_e
  val'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rails-erd-1.1.0/lib/rails_erd/diagram.rb:142:in `save'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rails-erd-1.1.0/lib/rails_erd/diagram.rb:120:in `create'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rails-erd-1.1.0/lib/rails_erd/diagram.rb:74:in `create'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rails-erd-1.1.0/lib/rails_erd/tasks.rake:41:in `block (2 le
  vels) in &lt;top (required)&gt;'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rake-10.0.3/lib/rake/task.rb:228:in `call'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rake-10.0.3/lib/rake/task.rb:228:in `block in execute'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rake-10.0.3/lib/rake/task.rb:223:in `each'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rake-10.0.3/lib/rake/task.rb:223:in `execute'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rake-10.0.3/lib/rake/task.rb:166:in `block in invoke_with_c
  all_chain'
  c:/Ruby193/lib/ruby/1.9.1/monitor.rb:211:in `mon_synchronize'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rake-10.0.3/lib/rake/task.rb:159:in `invoke_with_call_chain
  '
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rake-10.0.3/lib/rake/task.rb:187:in `block in invoke_prereq
  uisites'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rake-10.0.3/lib/rake/task.rb:185:in `each'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rake-10.0.3/lib/rake/task.rb:185:in `invoke_prerequisites'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rake-10.0.3/lib/rake/task.rb:165:in `block in invoke_with_c
  all_chain'
  c:/Ruby193/lib/ruby/1.9.1/monitor.rb:211:in `mon_synchronize'
  c:/Ruby193/lib/ruby/gems/1.9.1/gems/rake-10.0.3/lib/rake/task.rb:159:in `invoke_with_call_chain
  </code></pre>
  
  <p>Did any one have experience with such issues ?</p>