Redmine

I am using redmine 3.4.6 while is supported by plantuml plugin 0.5.1.

But after I copied the plugin into the folder and add a script into /usr/bin/plantuml. There are several issues

issue one:

when click the plugin configuration page, the error occurs

404
    The page you were trying to access doesn't exist or has been removed.

issue two:

because issue one, I can't set the default url of the "plantuml_binary_default", I modified the init.rb in the plugin folder. But where I paste the example code in the wiki, the error occurs:

Error executing the plantuml macro (uninitialized constant PlantumlHelper)

Here is the example code:

{{plantuml(png)
  Bob -> Alice : hello
}}

did I missed something in the installation? Any one successfully intergrated plantuml plugin in the redmine 3.4.6?