No, this is not a real Sinatra error :).
This is the personal homepage of Elad Meidar, a web developer and an entrepreneur specializing in Ruby on Rails. I hang around in Israel, and i am currently having the best time of my life over at Fiverr.com
I am a proud member of RailsBridge, Helping new Rails developers get into our world and also contributed a few Patches to the Ruby on Rails core.
There are certain standards we got used too when creating rails views and layouts, which may cause a problem or some set backs to our applications.
We are all used to coding the JS includes way up in our document, moving the JS to the bottom of the page will render your page a little bit faster, and this is why.
When a browser reads a page, it goes through from the top to the bottom, So when we put the JS include’s up, the browser will attempt to download them and hold the dom parsing until it finishes.
You're seeing this error because I think it is funny.