Lipsiadmin

I have downloaded demoadmin from the site.I am using Instant Rails 2.0.2.Whenever I am going to edit a new article I am getting following error:

Showing backend/articles/_form.html.erb where line #17 raised:

You have a nil object when you didn't expect it!
The error occurred while evaluating nil.width

Extracted source (around line #17):

14: -->
15: <div class="label">
16: <% if @article && @article.image >
17: <div class="boxImage" style="width:<= @article.image.get_thumbnail(:thumb).width >px;">
18: <div><= image_tag(@article.image.public_filename(:thumb)) ></div>
19: <div style="text-align:center;padding:5px"><= link_to "Destroy", {:action => :destroy_image, :id => @article}, {:confirm => "Are you sure to destroy this image?", :method => :delete} %></div>
20: </div>