Rails: Is the Problem compatibility of Project 1.8.7 to 1.9.2 or Mongrel/Thin

Question

I followed a starter tutorial for Rails 2 and created a project with Ruby 1.8.7 and it works with it. Unfortunatly, the project doesn't work as expected with Ruby 1.9.2 and gives errors. I'm not sure if Mongrel/webrick is the problem which seems not to work flawless with Ruby 1.9.2 or is it a problem with my code which doesn't suite 1.9.2. Otherwise there are the same problems when i use Thin with 1.9.2 with this project. It's a very simple beginner tutorial. The Rails Version is 2.34 Perhaps someone of you Pro's can help me?

 NoMethodError in Bookmarks#index

Showing app/views/layouts/application.html.erb where line #21 raised:

undefined method `^' for "c":String

Extracted source (around line #21):

21:       <% if flash[:notice] %>
22:           <%= flash[:notice] %>