In my fruitless efforts to get redmine running on IronRuby one of the things i discovered were that the lines like these: "field_done_ratio: % Done" in the locale yaml files throwed exceptions. if i removed the "%" it worked (or at least i went one step further).
 
(gave up after these 16hours, my last obstacle were infinite redirection while accessing localhost:3000/, although accessing localhost:3000/login went well, but after that you couldn't do anything.. )