diff --git a/app/models/submission.rb b/app/models/submission.rb
--- a/app/models/submission.rb
+++ b/app/models/submission.rb
@@ -154,7 +154,7 @@
       return if self.user.admin?
 
       #check if user has the right to submit the problem
-      errors.add('problem',"must be valid.") if (!self.user.available_problems.include?(self.problem)) and (self.new_record?)
+      errors[:base] << "Authorization error: you have no right to submit to this problem" if (!self.user.available_problems.include?(self.problem)) and (self.new_record?)
     end
   end