Problem installing flashplayrhelpr plugin

I’m trying to install the flashplayrhelpr plugin. I ran the following
at the command line, in my app’s root folder:

ruby script/plugin install svn://

A bunch of flash_player files got copied over to my app’s vendor/plugins
folder, and then it tries to install the flashplayrhelpr plugin, but

“Plugin not found: [“svn://”]”

Sure enough, i can’t use the helper commands in my app. If i force the
reinstall, i get the same message but without the flash_player stuff
being copied over.

This is definitely the given url for the plugin - has anyone else
managed this and can see what i’ve done wrong? Or had similar problems?
Or has a vague idea that can help? I’m using windows, in case that’s