The page contains some javascript. It might be possible that the page cannot be submitted without interpreting it. In such a case, you might be more lucky with WWW::Mechanize::Firefox.

Moreover, checking the documentation of WWW::Mechanize, I noticed that $browser->submit takes no parameters and returns a HTTP::Response object. Specifying

value => 'Run'
[download]

is debatable as well, since the button is not called "value" and its value is "RUN", not "Run".