Weird Rails 3 Route Problem

Hi,

I am using simple_captcha. It worked find until I add the following line
to routes.rb

match ":controller(/:action)", :constraints => {:controller =>
/sandbox\/[^\/]+/}

The captcha image is not showing and the log shows the following error
message.

Started GET
"/simple_captcha/8cdf70c193dc8823f281828f11c250e1739883da?time=1294644088"
for 127.0.0.1 at Sun Jan 09 23:21:29 -0800 2011

AbstractController::ActionNotFound (The action
'8cdf70c193dc8823f281828f11c250e1739883da' could not be found for
SimpleCaptchaController):

Why does the line in the routes affect simple_captcha?

Thanks.

Sam